package feature
Feature transformers
The ml.feature
package provides common feature transformers that help convert raw data or
features into more suitable forms for model fitting.
Most feature transformers are implemented as Transformers, which transform one DataFrame
into another, e.g., HashingTF.
Some feature transformers are implemented as Estimators, because the transformation requires
some aggregated information of the dataset, e.g., document frequencies in IDF.
For those feature transformers, calling Estimator.fit
is required to obtain the model first,
e.g., IDFModel, in order to apply transformation.
The transformation is usually done by appending new columns to the input DataFrame
, so all
input columns are carried over.
We try to make each transformer minimal, so it becomes flexible to assemble feature transformation pipelines. Pipeline can be used to chain feature transformers, and VectorAssembler can be used to combine multiple feature transformations, for example:
import org.apache.spark.ml.feature._ import org.apache.spark.ml.Pipeline // a DataFrame with three columns: id (integer), text (string), and rating (double). val df = spark.createDataFrame(Seq( (0, "Hi I heard about Spark", 3.0), (1, "I wish Java could use case classes", 4.0), (2, "Logistic regression models are neat", 4.0) )).toDF("id", "text", "rating") // define feature transformers val tok = new RegexTokenizer() .setInputCol("text") .setOutputCol("words") val sw = new StopWordsRemover() .setInputCol("words") .setOutputCol("filtered_words") val tf = new HashingTF() .setInputCol("filtered_words") .setOutputCol("tf") .setNumFeatures(10000) val idf = new IDF() .setInputCol("tf") .setOutputCol("tf_idf") val assembler = new VectorAssembler() .setInputCols(Array("tf_idf", "rating")) .setOutputCol("features") // assemble and fit the feature transformation pipeline val pipeline = new Pipeline() .setStages(Array(tok, sw, tf, idf, assembler)) val model = pipeline.fit(df) // save transformed features with raw data model.transform(df) .select("id", "text", "rating", "features") .write.format("parquet").save("/output/path")
Some feature transformers implemented in MLlib are inspired by those implemented in scikitlearn. The major difference is that most scikitlearn feature transformers operate eagerly on the entire input dataset, while MLlib's feature transformers operate lazily on individual columns, which is more efficient and flexible to handle large and complex datasets.
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final
class
Binarizer extends Transformer with HasThreshold with HasThresholds with HasInputCol with HasOutputCol with HasInputCols with HasOutputCols with DefaultParamsWritable
Binarize a column of continuous features given a threshold.
Binarize a column of continuous features given a threshold.
Since 3.0.0,
Binarize
can map multiple columns at once by setting theinputCols
parameter. Note that when both theinputCol
andinputCols
parameters are set, an Exception will be thrown. Thethreshold
parameter is used for single column usage, andthresholds
is for multiple columns. Annotations
 @Since( "1.4.0" )

class
BucketedRandomProjectionLSH extends LSH[BucketedRandomProjectionLSHModel] with BucketedRandomProjectionLSHParams with HasSeed
This BucketedRandomProjectionLSH implements Locality Sensitive Hashing functions for Euclidean distance metrics.
This BucketedRandomProjectionLSH implements Locality Sensitive Hashing functions for Euclidean distance metrics.
The input is dense or sparse vectors, each of which represents a point in the Euclidean distance space. The output will be vectors of configurable dimension. Hash values in the same dimension are calculated by the same hash function.
References:
1. Wikipedia on Stable Distributions
2. Wang, Jingdong et al. "Hashing for similarity search: A survey." arXiv preprint arXiv:1408.2927 (2014).
 Annotations
 @Since( "2.1.0" )

class
BucketedRandomProjectionLSHModel extends LSHModel[BucketedRandomProjectionLSHModel] with BucketedRandomProjectionLSHParams
Model produced by BucketedRandomProjectionLSH, where multiple random vectors are stored.
Model produced by BucketedRandomProjectionLSH, where multiple random vectors are stored. The vectors are normalized to be unit vectors and each vector is used in a hash function:
h_i(x) = floor(r_i.dot(x) / bucketLength)
wherer_i
is the ith random unit vector. The number of buckets will be(max L2 norm of input vectors) / bucketLength
. Annotations
 @Since( "2.1.0" )

final
class
Bucketizer extends Model[Bucketizer] with HasHandleInvalid with HasInputCol with HasOutputCol with HasInputCols with HasOutputCols with DefaultParamsWritable
Bucketizer
maps a column of continuous features to a column of feature buckets.Bucketizer
maps a column of continuous features to a column of feature buckets.Since 2.3.0,
Bucketizer
can map multiple columns at once by setting theinputCols
parameter. Note that when both theinputCol
andinputCols
parameters are set, an Exception will be thrown. Thesplits
parameter is only used for single column usage, andsplitsArray
is for multiple columns. Annotations
 @Since( "1.4.0" )

final
class
ChiSqSelectorModel extends SelectorModel[ChiSqSelectorModel]
Model fitted by ChiSqSelector.
Model fitted by ChiSqSelector.
 Annotations
 @Since( "1.6.0" )

class
CountVectorizer extends Estimator[CountVectorizerModel] with CountVectorizerParams with DefaultParamsWritable
Extracts a vocabulary from document collections and generates a CountVectorizerModel.
Extracts a vocabulary from document collections and generates a CountVectorizerModel.
 Annotations
 @Since( "1.5.0" )

class
CountVectorizerModel extends Model[CountVectorizerModel] with CountVectorizerParams with MLWritable
Converts a text document to a sparse vector of token counts.
Converts a text document to a sparse vector of token counts.
 Annotations
 @Since( "1.5.0" )

class
DCT extends UnaryTransformer[Vector, Vector, DCT] with DefaultParamsWritable
A feature transformer that takes the 1D discrete cosine transform of a real vector.
A feature transformer that takes the 1D discrete cosine transform of a real vector. No zero padding is performed on the input vector. It returns a real vector of the same length representing the DCT. The return vector is scaled such that the transform matrix is unitary (aka scaled DCTII).
More information on DCTII in Discrete cosine transform (Wikipedia).
 Annotations
 @Since( "1.5.0" )

class
ElementwiseProduct extends UnaryTransformer[Vector, Vector, ElementwiseProduct] with DefaultParamsWritable
Outputs the Hadamard product (i.e., the elementwise product) of each input vector with a provided "weight" vector.
Outputs the Hadamard product (i.e., the elementwise product) of each input vector with a provided "weight" vector. In other words, it scales each column of the dataset by a scalar multiplier.
 Annotations
 @Since( "1.4.0" )

class
FeatureHasher extends Transformer with HasInputCols with HasOutputCol with HasNumFeatures with DefaultParamsWritable
Feature hashing projects a set of categorical or numerical features into a feature vector of specified dimension (typically substantially smaller than that of the original feature space).
Feature hashing projects a set of categorical or numerical features into a feature vector of specified dimension (typically substantially smaller than that of the original feature space). This is done using the hashing trick (https://en.wikipedia.org/wiki/Feature_hashing) to map features to indices in the feature vector.
The FeatureHasher transformer operates on multiple columns. Each column may contain either numeric or categorical features. Behavior and handling of column data types is as follows: Numeric columns: For numeric features, the hash value of the column name is used to map the feature value to its index in the feature vector. By default, numeric features are not treated as categorical (even when they are integers). To treat them as categorical, specify the relevant columns in
categoricalCols
. String columns: For categorical features, the hash value of the string "column_name=value" is used to map to the vector index, with an indicator value of1.0
. Thus, categorical features are "onehot" encoded (similarly to using OneHotEncoder withdropLast=false
). Boolean columns: Boolean values are treated in the same way as string columns. That is, boolean features are represented as "column_name=true" or "column_name=false", with an indicator value of1.0
.Null (missing) values are ignored (implicitly zero in the resulting feature vector).
The hash function used here is also the MurmurHash 3 used in HashingTF. Since a simple modulo on the hashed value is used to determine the vector index, it is advisable to use a power of two as the numFeatures parameter; otherwise the features will not be mapped evenly to the vector indices.
val df = Seq( (2.0, true, "1", "foo"), (3.0, false, "2", "bar") ).toDF("real", "bool", "stringNum", "string") val hasher = new FeatureHasher() .setInputCols("real", "bool", "stringNum", "string") .setOutputCol("features") hasher.transform(df).show(false) ++++++ realbool stringNumstringfeatures  ++++++ 2.0 true 1 foo (262144,[51871,63643,174475,253195],[1.0,1.0,2.0,1.0]) 3.0 false2 bar (262144,[6031,80619,140467,174475],[1.0,1.0,1.0,3.0])  ++++++
 Annotations
 @Since( "2.3.0" )

class
HashingTF extends Transformer with HasInputCol with HasOutputCol with HasNumFeatures with DefaultParamsWritable
Maps a sequence of terms to their term frequencies using the hashing trick.
Maps a sequence of terms to their term frequencies using the hashing trick. Currently we use Austin Appleby's MurmurHash 3 algorithm (MurmurHash3_x86_32) to calculate the hash code value for the term object. Since a simple modulo is used to transform the hash function to a column index, it is advisable to use a power of two as the numFeatures parameter; otherwise the features will not be mapped evenly to the columns.
 Annotations
 @Since( "1.2.0" )

final
class
IDF extends Estimator[IDFModel] with IDFBase with DefaultParamsWritable
Compute the Inverse Document Frequency (IDF) given a collection of documents.
Compute the Inverse Document Frequency (IDF) given a collection of documents.
 Annotations
 @Since( "1.4.0" )

class
IDFModel extends Model[IDFModel] with IDFBase with MLWritable
Model fitted by IDF.
Model fitted by IDF.
 Annotations
 @Since( "1.4.0" )

class
Imputer extends Estimator[ImputerModel] with ImputerParams with DefaultParamsWritable
Imputation estimator for completing missing values, using the mean, median or mode of the columns in which the missing values are located.
Imputation estimator for completing missing values, using the mean, median or mode of the columns in which the missing values are located. The input columns should be of numeric type. Currently Imputer does not support categorical features (SPARK15041) and possibly creates incorrect values for a categorical feature.
Note when an input column is integer, the imputed value is casted (truncated) to an integer type. For example, if the input column is IntegerType (1, 2, 4, null), the output will be IntegerType (1, 2, 4, 2) after mean imputation.
Note that the mean/median/mode value is computed after filtering out missing values. All Null values in the input columns are treated as missing, and so are also imputed. For computing median, DataFrameStatFunctions.approxQuantile is used with a relative error of 0.001.
 Annotations
 @Since( "2.2.0" )

class
ImputerModel extends Model[ImputerModel] with ImputerParams with MLWritable
Model fitted by Imputer.
Model fitted by Imputer.
 Annotations
 @Since( "2.2.0" )

class
IndexToString extends Transformer with HasInputCol with HasOutputCol with DefaultParamsWritable
A
Transformer
that maps a column of indices back to a new column of corresponding string values.A
Transformer
that maps a column of indices back to a new column of corresponding string values. The indexstring mapping is either from the ML attributes of the input column, or from usersupplied labels (which take precedence over ML attributes). Annotations
 @Since( "1.5.0" )
 See also
StringIndexer
for converting strings into indices

class
Interaction extends Transformer with HasInputCols with HasOutputCol with DefaultParamsWritable
Implements the feature interaction transform.
Implements the feature interaction transform. This transformer takes in Double and Vector type columns and outputs a flattened vector of their feature interactions. To handle interaction, we first onehot encode any nominal features. Then, a vector of the feature crossproducts is produced.
For example, given the input feature values
Double(2)
andVector(3, 4)
, the output would beVector(6, 8)
if all input features were numeric. If the first feature was instead nominal with four categories, the output would then beVector(0, 0, 0, 0, 3, 4, 0, 0)
. Annotations
 @Since( "1.6.0" )

case class
LabeledPoint(label: Double, features: Vector) extends Product with Serializable
Class that represents the features and label of a data point.
Class that represents the features and label of a data point.
 label
Label for this data point.
 features
List of features for this data point.
 Annotations
 @Since( "2.0.0" )

class
MaxAbsScaler extends Estimator[MaxAbsScalerModel] with MaxAbsScalerParams with DefaultParamsWritable
Rescale each feature individually to range [1, 1] by dividing through the largest maximum absolute value in each feature.
Rescale each feature individually to range [1, 1] by dividing through the largest maximum absolute value in each feature. It does not shift/center the data, and thus does not destroy any sparsity.
 Annotations
 @Since( "2.0.0" )

class
MaxAbsScalerModel extends Model[MaxAbsScalerModel] with MaxAbsScalerParams with MLWritable
Model fitted by MaxAbsScaler.
Model fitted by MaxAbsScaler.
 Annotations
 @Since( "2.0.0" )

class
MinHashLSH extends LSH[MinHashLSHModel] with HasSeed
LSH class for Jaccard distance.
LSH class for Jaccard distance.
The input can be dense or sparse vectors, but it is more efficient if it is sparse. For example,
Vectors.sparse(10, Array((2, 1.0), (3, 1.0), (5, 1.0)))
means there are 10 elements in the space. This set contains elements 2, 3, and 5. Also, any input vector must have at least 1 nonzero index, and all nonzero values are treated as binary "1" values.References: Wikipedia on MinHash
 Annotations
 @Since( "2.1.0" )

class
MinHashLSHModel extends LSHModel[MinHashLSHModel]
Model produced by MinHashLSH, where multiple hash functions are stored.
Model produced by MinHashLSH, where multiple hash functions are stored. Each hash function is picked from the following family of hash functions, where a_i and b_i are randomly chosen integers less than prime:
h_i(x) = ((x \cdot a_i + b_i) \mod prime)
This hash family is approximately minwise independent according to the reference.
Reference: Tom Bohman, Colin Cooper, and Alan Frieze. "Minwise independent linear permutations." Electronic Journal of Combinatorics 7 (2000): R26.
 Annotations
 @Since( "2.1.0" )

class
MinMaxScaler extends Estimator[MinMaxScalerModel] with MinMaxScalerParams with DefaultParamsWritable
Rescale each feature individually to a common range [min, max] linearly using column summary statistics, which is also known as minmax normalization or Rescaling.
Rescale each feature individually to a common range [min, max] linearly using column summary statistics, which is also known as minmax normalization or Rescaling. The rescaled value for feature E is calculated as:
$$ Rescaled(e_i) = \frac{e_i  E_{min}}{E_{max}  E_{min}} * (max  min) + min $$
For the case \(E_{max} == E_{min}\), \(Rescaled(e_i) = 0.5 * (max + min)\).
 Annotations
 @Since( "1.5.0" )
 Note
Since zero values will probably be transformed to nonzero values, output of the transformer will be DenseVector even for sparse input.

class
MinMaxScalerModel extends Model[MinMaxScalerModel] with MinMaxScalerParams with MLWritable
Model fitted by MinMaxScaler.
Model fitted by MinMaxScaler.
 Annotations
 @Since( "1.5.0" )

class
NGram extends UnaryTransformer[Seq[String], Seq[String], NGram] with DefaultParamsWritable
A feature transformer that converts the input array of strings into an array of ngrams.
A feature transformer that converts the input array of strings into an array of ngrams. Null values in the input array are ignored. It returns an array of ngrams where each ngram is represented by a spaceseparated string of words.
When the input is empty, an empty array is returned. When the input array length is less than n (number of elements per ngram), no ngrams are returned.
 Annotations
 @Since( "1.5.0" )

class
Normalizer extends UnaryTransformer[Vector, Vector, Normalizer] with DefaultParamsWritable
Normalize a vector to have unit norm using the given pnorm.
Normalize a vector to have unit norm using the given pnorm.
 Annotations
 @Since( "1.4.0" )

class
OneHotEncoder extends Estimator[OneHotEncoderModel] with OneHotEncoderBase with DefaultParamsWritable
A onehot encoder that maps a column of category indices to a column of binary vectors, with at most a single onevalue per row that indicates the input category index.
A onehot encoder that maps a column of category indices to a column of binary vectors, with at most a single onevalue per row that indicates the input category index. For example with 5 categories, an input value of 2.0 would map to an output vector of
[0.0, 0.0, 1.0, 0.0]
. The last category is not included by default (configurable viadropLast
), because it makes the vector entries sum up to one, and hence linearly dependent. So an input value of 4.0 maps to[0.0, 0.0, 0.0, 0.0]
. Annotations
 @Since( "3.0.0" )
 Note
This is different from scikitlearn's OneHotEncoder, which keeps all categories. The output vectors are sparse. When
,handleInvalid
is configured to 'keep', an extra "category" indicating invalid values is added as last category. So whendropLast
is true, invalid values are encoded as allzeros vector.When encoding multicolumn by using
inputCols
andoutputCols
params, input/output cols come in pairs, specified by the order in the arrays, and each pair is treated independently. See also
StringIndexer
for converting categorical values into category indices

class
OneHotEncoderModel extends Model[OneHotEncoderModel] with OneHotEncoderBase with MLWritable
 Annotations
 @Since( "3.0.0" )

class
PCA extends Estimator[PCAModel] with PCAParams with DefaultParamsWritable
PCA trains a model to project vectors to a lower dimensional space of the top
PCA!.k
principal components.PCA trains a model to project vectors to a lower dimensional space of the top
PCA!.k
principal components. Annotations
 @Since( "1.5.0" )

class
PCAModel extends Model[PCAModel] with PCAParams with MLWritable
Model fitted by PCA.
Model fitted by PCA. Transforms vectors to a lower dimensional space.
 Annotations
 @Since( "1.5.0" )

class
PolynomialExpansion extends UnaryTransformer[Vector, Vector, PolynomialExpansion] with DefaultParamsWritable
Perform feature expansion in a polynomial space.
Perform feature expansion in a polynomial space. As said in wikipedia of Polynomial Expansion, which is available at Polynomial expansion (Wikipedia) , "In mathematics, an expansion of a product of sums expresses it as a sum of products by using the fact that multiplication distributes over addition". Take a 2variable feature vector as an example:
(x, y)
, if we want to expand it with degree 2, then we get(x, x * x, y, x * y, y * y)
. Annotations
 @Since( "1.4.0" )

final
class
QuantileDiscretizer extends Estimator[Bucketizer] with QuantileDiscretizerBase with DefaultParamsWritable
QuantileDiscretizer
takes a column with continuous features and outputs a column with binned categorical features.QuantileDiscretizer
takes a column with continuous features and outputs a column with binned categorical features. The number of bins can be set using thenumBuckets
parameter. It is possible that the number of buckets used will be smaller than this value, for example, if there are too few distinct values of the input to create enough distinct quantiles. Since 2.3.0,QuantileDiscretizer
can map multiple columns at once by setting theinputCols
parameter. If both of theinputCol
andinputCols
parameters are set, an Exception will be thrown. To specify the number of buckets for each column, thenumBucketsArray
parameter can be set, or if the number of buckets should be the same across columns,numBuckets
can be set as a convenience. Note that in multiple columns case, relative error is applied to all columns.NaN handling: null and NaN values will be ignored from the column during
QuantileDiscretizer
fitting. This will produce aBucketizer
model for making predictions. During the transformation,Bucketizer
will raise an error when it finds NaN values in the dataset, but the user can also choose to either keep or remove NaN values within the dataset by settinghandleInvalid
. If the user chooses to keep NaN values, they will be handled specially and placed into their own bucket, for example, if 4 buckets are used, then nonNaN data will be put into buckets[03], but NaNs will be counted in a special bucket[4].Algorithm: The bin ranges are chosen using an approximate algorithm (see the documentation for
org.apache.spark.sql.DataFrameStatFunctions.approxQuantile
for a detailed description). The precision of the approximation can be controlled with therelativeError
parameter. The lower and upper bin bounds will beInfinity
and+Infinity
, covering all real values. Annotations
 @Since( "1.6.0" )

class
RFormula extends Estimator[RFormulaModel] with RFormulaBase with DefaultParamsWritable
Implements the transforms required for fitting a dataset against an R model formula.
Implements the transforms required for fitting a dataset against an R model formula. Currently we support a limited subset of the R operators, including '~', '.', ':', '+', '', '*' and '^'. Also see the R formula docs here: http://stat.ethz.ch/Rmanual/Rpatched/library/stats/html/formula.html
The basic operators are:
~
separate target and terms+
concat terms, "+ 0" means removing intercept
remove a term, " 1" means removing intercept:
interaction (multiplication for numeric values, or binarized categorical values).
all columns except target*
factor crossing, includes the terms and interactions between them^
factor crossing to a specified degree
Suppose
a
andb
are double columns, we use the following simple examples to illustrate the effect ofRFormula
:y ~ a + b
means modely ~ w0 + w1 * a + w2 * b
wherew0
is the intercept andw1, w2
are coefficients.y ~ a + b + a:b  1
means modely ~ w1 * a + w2 * b + w3 * a * b
wherew1, w2, w3
are coefficients.y ~ a * b
means modely ~ w0 + w1 * a + w2 * b + w3 * a * b
wherew0
is the intercept andw1, w2, w3
are coefficientsy ~ (a + b)^2
means model
y ~ w0 + w1 * a + w2 * b + w3 * a * bwhere
w0is the intercept and
w1, w2, w3are coefficients
RFormula produces a vector column of features and a double or string column of label. Like when formulas are used in R for linear regression, string input columns will be onehot encoded, and numeric columns will be cast to doubles. If the label column is of type string, it will be first transformed to double with
StringIndexer
. If the label column does not exist in the DataFrame, the output label column will be created from the specified response variable in the formula. Annotations
 @Since( "1.5.0" )

class
RFormulaModel extends Model[RFormulaModel] with RFormulaBase with MLWritable
Model fitted by RFormula.
Model fitted by RFormula. Fitting is required to determine the factor levels of formula terms.
 Annotations
 @Since( "1.5.0" )

class
RegexTokenizer extends UnaryTransformer[String, Seq[String], RegexTokenizer] with DefaultParamsWritable
A regex based tokenizer that extracts tokens either by using the provided regex pattern to split the text (default) or repeatedly matching the regex (if
gaps
is false).A regex based tokenizer that extracts tokens either by using the provided regex pattern to split the text (default) or repeatedly matching the regex (if
gaps
is false). Optional parameters also allow filtering tokens using a minimal length. It returns an array of strings that can be empty. Annotations
 @Since( "1.4.0" )

class
RobustScaler extends Estimator[RobustScalerModel] with RobustScalerParams with DefaultParamsWritable
Scale features using statistics that are robust to outliers.
Scale features using statistics that are robust to outliers. RobustScaler removes the median and scales the data according to the quantile range. The quantile range is by default IQR (Interquartile Range, quantile range between the 1st quartile = 25th quantile and the 3rd quartile = 75th quantile) but can be configured. Centering and scaling happen independently on each feature by computing the relevant statistics on the samples in the training set. Median and quantile range are then stored to be used on later data using the transform method. Standardization of a dataset is a common requirement for many machine learning estimators. Typically this is done by removing the mean and scaling to unit variance. However, outliers can often influence the sample mean / variance in a negative way. In such cases, the median and the quantile range often give better results. Note that NaN values are ignored in the computation of medians and ranges.
 Annotations
 @Since( "3.0.0" )

class
RobustScalerModel extends Model[RobustScalerModel] with RobustScalerParams with MLWritable
Model fitted by RobustScaler.
Model fitted by RobustScaler.
 Annotations
 @Since( "3.0.0" )

class
SQLTransformer extends Transformer with DefaultParamsWritable
Implements the transformations which are defined by SQL statement.
Implements the transformations which are defined by SQL statement. Currently we only support SQL syntax like 'SELECT ... FROM THIS ...' where 'THIS' represents the underlying table of the input dataset. The select clause specifies the fields, constants, and expressions to display in the output, it can be any select clause that Spark SQL supports. Users can also use Spark SQL builtin function and UDFs to operate on these selected columns. For example, SQLTransformer supports statements like:
SELECT a, a + b AS a_b FROM __THIS__ SELECT a, SQRT(b) AS b_sqrt FROM __THIS__ where a > 5 SELECT a, b, SUM(c) AS c_sum FROM __THIS__ GROUP BY a, b
 Annotations
 @Since( "1.6.0" )

class
StandardScaler extends Estimator[StandardScalerModel] with StandardScalerParams with DefaultParamsWritable
Standardizes features by removing the mean and scaling to unit variance using column summary statistics on the samples in the training set.
Standardizes features by removing the mean and scaling to unit variance using column summary statistics on the samples in the training set.
The "unit std" is computed using the corrected sample standard deviation, which is computed as the square root of the unbiased sample variance.
 Annotations
 @Since( "1.2.0" )

class
StandardScalerModel extends Model[StandardScalerModel] with StandardScalerParams with MLWritable
Model fitted by StandardScaler.
Model fitted by StandardScaler.
 Annotations
 @Since( "1.2.0" )

class
StopWordsRemover extends Transformer with HasInputCol with HasOutputCol with HasInputCols with HasOutputCols with DefaultParamsWritable
A feature transformer that filters out stop words from input.
A feature transformer that filters out stop words from input.
Since 3.0.0,
StopWordsRemover
can filter out multiple columns at once by setting theinputCols
parameter. Note that when both theinputCol
andinputCols
parameters are set, an Exception will be thrown. Annotations
 @Since( "1.5.0" )
 Note
null values from input array are preserved unless adding null to stopWords explicitly.
 See also

class
StringIndexer extends Estimator[StringIndexerModel] with StringIndexerBase with DefaultParamsWritable
A label indexer that maps string column(s) of labels to ML column(s) of label indices.
A label indexer that maps string column(s) of labels to ML column(s) of label indices. If the input columns are numeric, we cast them to string and index the string values. The indices are in [0, numLabels). By default, this is ordered by label frequencies so the most frequent label gets index 0. The ordering behavior is controlled by setting
stringOrderType
. Annotations
 @Since( "1.4.0" )
 See also
IndexToString
for the inverse transformation

class
StringIndexerModel extends Model[StringIndexerModel] with StringIndexerBase with MLWritable
Model fitted by StringIndexer.
Model fitted by StringIndexer.
 Annotations
 @Since( "1.4.0" )
 Note
During transformation, if any input column does not exist,
StringIndexerModel.transform
would skip the input column. If all input columns do not exist, it returns the input dataset unmodified. This is a temporary fix for the case when target labels do not exist during prediction.

class
Tokenizer extends UnaryTransformer[String, Seq[String], Tokenizer] with DefaultParamsWritable
A tokenizer that converts the input string to lowercase and then splits it by white spaces.
A tokenizer that converts the input string to lowercase and then splits it by white spaces.
 Annotations
 @Since( "1.2.0" )
 See also

final
class
UnivariateFeatureSelector extends Estimator[UnivariateFeatureSelectorModel] with UnivariateFeatureSelectorParams with DefaultParamsWritable
The user can set
featureType
and labelType, and Spark will pick the score function based on the specified
featureTypeand labelType
.The user can set
featureType
and labelType, and Spark will pick the score function based on the specified
featureTypeand labelType
. The following combination offeatureType
andlabelType
are supported:featureType
categorical
andlabelType
categorical
: Spark uses chisquared, i.e. chi2 in sklearn.featureType
continuous
andlabelType
categorical
: Spark uses ANOVATest, i.e. f_classif in sklearn.featureType
continuous
andlabelType
continuous
: Spark uses Fvalue, i.e. f_regression in sklearn.
The
UnivariateFeatureSelector
supports different selection modes:numTopFeatures
,percentile
,fpr
,fdr
,fwe
.numTopFeatures
chooses a fixed number of top features according to a hypothesis.percentile
is similar but chooses a fraction of all features instead of a fixed number.fpr
chooses all features whose pvalue are below a threshold, thus controlling the false positive rate of selection.fdr
uses the BenjaminiHochberg procedure to choose all features whose false discovery rate is below a threshold.fwe
chooses all features whose pvalues are below a threshold. The threshold is scaled by 1/numFeatures, thus controlling the familywise error rate of selection.
By default, the selection mode is
numTopFeatures
. Annotations
 @Since( "3.1.1" )

class
UnivariateFeatureSelectorModel extends Model[UnivariateFeatureSelectorModel] with UnivariateFeatureSelectorParams with MLWritable
Model fitted by UnivariateFeatureSelectorModel.
Model fitted by UnivariateFeatureSelectorModel.
 Annotations
 @Since( "3.1.1" )

final
class
VarianceThresholdSelector extends Estimator[VarianceThresholdSelectorModel] with VarianceThresholdSelectorParams with DefaultParamsWritable
Feature selector that removes all lowvariance features.
Feature selector that removes all lowvariance features. Features with a variance not greater than the threshold will be removed. The default is to keep all features with nonzero variance, i.e. remove the features that have the same value in all samples.
 Annotations
 @Since( "3.1.0" )

class
VarianceThresholdSelectorModel extends Model[VarianceThresholdSelectorModel] with VarianceThresholdSelectorParams with MLWritable
Model fitted by VarianceThresholdSelector.
Model fitted by VarianceThresholdSelector.
 Annotations
 @Since( "3.1.0" )

class
VectorAssembler extends Transformer with HasInputCols with HasOutputCol with HasHandleInvalid with DefaultParamsWritable
A feature transformer that merges multiple columns into a vector column.
A feature transformer that merges multiple columns into a vector column.
This requires one pass over the entire dataset. In case we need to infer column lengths from the data we require an additional call to the 'first' Dataset method, see 'handleInvalid' parameter.
 Annotations
 @Since( "1.4.0" )

class
VectorIndexer extends Estimator[VectorIndexerModel] with VectorIndexerParams with DefaultParamsWritable
Class for indexing categorical feature columns in a dataset of
Vector
.Class for indexing categorical feature columns in a dataset of
Vector
.This has 2 usage modes:
 Automatically identify categorical features (default behavior)
 This helps process a dataset of unknown vectors into a dataset with some continuous features and some categorical features. The choice between continuous and categorical is based upon a maxCategories parameter.
 Set maxCategories to the maximum number of categorical any categorical feature should have.
 E.g.: Feature 0 has unique values {1.0, 0.0}, and feature 1 values {1.0, 3.0, 5.0}. If maxCategories = 2, then feature 0 will be declared categorical and use indices {0, 1}, and feature 1 will be declared continuous.
 Index all features, if all features are categorical
 If maxCategories is set to be very large, then this will build an index of unique values for all features.
 Warning: This can cause problems if features are continuous since this will collect ALL unique values to the driver.
 E.g.: Feature 0 has unique values {1.0, 0.0}, and feature 1 values {1.0, 3.0, 5.0}. If maxCategories is greater than or equal to 3, then both features will be declared categorical.
This returns a model which can transform categorical features to use 0based indices.
Index stability:
 This is not guaranteed to choose the same category index across multiple runs.
 If a categorical feature includes value 0, then this is guaranteed to map value 0 to index 0. This maintains vector sparsity.
 More stability may be added in the future.
TODO: Future extensions: The following functionality is planned for the future:
 Preserve metadata in transform; if a feature's metadata is already present, do not recompute.
 Specify certain features to not index, either via a parameter or via existing metadata.
 Add warning if a categorical feature has only 1 category.
 Annotations
 @Since( "1.4.0" )
 Automatically identify categorical features (default behavior)

class
VectorIndexerModel extends Model[VectorIndexerModel] with VectorIndexerParams with MLWritable
Model fitted by VectorIndexer.
Model fitted by VectorIndexer. Transform categorical features to use 0based indices instead of their original values.
 Categorical features are mapped to indices.
 Continuous features (columns) are left unchanged. This also appends metadata to the output column, marking features as Numeric (continuous), Nominal (categorical), or Binary (either continuous or categorical). NonML metadata is not carried over from the input to the output column.
This maintains vector sparsity.
 Annotations
 @Since( "1.4.0" )

class
VectorSizeHint extends Transformer with HasInputCol with HasHandleInvalid with DefaultParamsWritable
A feature transformer that adds size information to the metadata of a vector column.
A feature transformer that adds size information to the metadata of a vector column. VectorAssembler needs size information for its input columns and cannot be used on streaming dataframes without this metadata.
Note: VectorSizeHint modifies
inputCol
to include size metadata and does not have an outputCol. Annotations
 @Since( "2.3.0" )

final
class
VectorSlicer extends Transformer with HasInputCol with HasOutputCol with DefaultParamsWritable
This class takes a feature vector and outputs a new feature vector with a subarray of the original features.
This class takes a feature vector and outputs a new feature vector with a subarray of the original features.
The subset of features can be specified with either indices (
setIndices()
) or names (setNames()
). At least one feature must be selected. Duplicate features are not allowed, so there can be no overlap between selected indices and names.The output vector will order features with the selected indices first (in the order given), followed by the selected names (in the order given).
 Annotations
 @Since( "1.5.0" )

final
class
Word2Vec extends Estimator[Word2VecModel] with Word2VecBase with DefaultParamsWritable
Word2Vec trains a model of
Map(String, Vector)
, i.e.Word2Vec trains a model of
Map(String, Vector)
, i.e. transforms a word into a code for further natural language processing or machine learning process. Annotations
 @Since( "1.4.0" )

class
Word2VecModel extends Model[Word2VecModel] with Word2VecBase with MLWritable
Model fitted by Word2Vec.
Model fitted by Word2Vec.
 Annotations
 @Since( "1.4.0" )

final
class
ChiSqSelector extends Selector[ChiSqSelectorModel]
ChiSquared feature selection, which selects categorical features to use for predicting a categorical label.
ChiSquared feature selection, which selects categorical features to use for predicting a categorical label. The selector supports different selection methods:
numTopFeatures
,percentile
,fpr
,fdr
,fwe
.numTopFeatures
chooses a fixed number of top features according to a chisquared test.percentile
is similar but chooses a fraction of all features instead of a fixed number.fpr
chooses all features whose pvalue are below a threshold, thus controlling the false positive rate of selection.fdr
uses the [BenjaminiHochberg procedure] (https://en.wikipedia.org/wiki/False_discovery_rate#Benjamini.E2.80.93Hochberg_procedure) to choose all features whose false discovery rate is below a threshold.fwe
chooses all features whose pvalues are below a threshold. The threshold is scaled by 1/numFeatures, thus controlling the familywise error rate of selection. By default, the selection method isnumTopFeatures
, with the default number of top features set to 50.
 Annotations
 @deprecated @Since( "1.6.0" )
 Deprecated
(Since version 3.1.1) use UnivariateFeatureSelector instead
Value Members

object
Binarizer extends DefaultParamsReadable[Binarizer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
BucketedRandomProjectionLSH extends DefaultParamsReadable[BucketedRandomProjectionLSH] with Serializable
 Annotations
 @Since( "2.1.0" )

object
BucketedRandomProjectionLSHModel extends MLReadable[BucketedRandomProjectionLSHModel] with Serializable
 Annotations
 @Since( "2.1.0" )

object
Bucketizer extends DefaultParamsReadable[Bucketizer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
ChiSqSelector extends DefaultParamsReadable[ChiSqSelector] with Serializable
 Annotations
 @Since( "1.6.0" )

object
ChiSqSelectorModel extends MLReadable[ChiSqSelectorModel] with Serializable
 Annotations
 @Since( "1.6.0" )

object
CountVectorizer extends DefaultParamsReadable[CountVectorizer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
CountVectorizerModel extends MLReadable[CountVectorizerModel] with Serializable
 Annotations
 @Since( "1.6.0" )

object
DCT extends DefaultParamsReadable[DCT] with Serializable
 Annotations
 @Since( "1.6.0" )

object
ElementwiseProduct extends DefaultParamsReadable[ElementwiseProduct] with Serializable
 Annotations
 @Since( "2.0.0" )

object
FeatureHasher extends DefaultParamsReadable[FeatureHasher] with Serializable
 Annotations
 @Since( "2.3.0" )

object
HashingTF extends DefaultParamsReadable[HashingTF] with Serializable
 Annotations
 @Since( "1.6.0" )

object
IDF extends DefaultParamsReadable[IDF] with Serializable
 Annotations
 @Since( "1.6.0" )

object
IDFModel extends MLReadable[IDFModel] with Serializable
 Annotations
 @Since( "1.6.0" )

object
Imputer extends DefaultParamsReadable[Imputer] with Serializable
 Annotations
 @Since( "2.2.0" )

object
ImputerModel extends MLReadable[ImputerModel] with Serializable
 Annotations
 @Since( "2.2.0" )

object
IndexToString extends DefaultParamsReadable[IndexToString] with Serializable
 Annotations
 @Since( "1.6.0" )

object
Interaction extends DefaultParamsReadable[Interaction] with Serializable
 Annotations
 @Since( "1.6.0" )

object
MaxAbsScaler extends DefaultParamsReadable[MaxAbsScaler] with Serializable
 Annotations
 @Since( "2.0.0" )

object
MaxAbsScalerModel extends MLReadable[MaxAbsScalerModel] with Serializable
 Annotations
 @Since( "2.0.0" )

object
MinHashLSH extends DefaultParamsReadable[MinHashLSH] with Serializable
 Annotations
 @Since( "2.1.0" )

object
MinHashLSHModel extends MLReadable[MinHashLSHModel] with Serializable
 Annotations
 @Since( "2.1.0" )

object
MinMaxScaler extends DefaultParamsReadable[MinMaxScaler] with Serializable
 Annotations
 @Since( "1.6.0" )

object
MinMaxScalerModel extends MLReadable[MinMaxScalerModel] with Serializable
 Annotations
 @Since( "1.6.0" )

object
NGram extends DefaultParamsReadable[NGram] with Serializable
 Annotations
 @Since( "1.6.0" )

object
Normalizer extends DefaultParamsReadable[Normalizer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
OneHotEncoder extends DefaultParamsReadable[OneHotEncoder] with Serializable
 Annotations
 @Since( "3.0.0" )

object
OneHotEncoderModel extends MLReadable[OneHotEncoderModel] with Serializable
 Annotations
 @Since( "3.0.0" )

object
PCA extends DefaultParamsReadable[PCA] with Serializable
 Annotations
 @Since( "1.6.0" )

object
PCAModel extends MLReadable[PCAModel] with Serializable
 Annotations
 @Since( "1.6.0" )

object
PolynomialExpansion extends DefaultParamsReadable[PolynomialExpansion] with Serializable
The expansion is done via recursion.
The expansion is done via recursion. Given n features and degree d, the size after expansion is (n + d choose d) (including 1 and firstorder values). For example, let f([a, b, c], 3) be the function that expands [a, b, c] to their monomials of degree 3. We have the following recursion:
$$ f([a, b, c], 3) &= f([a, b], 3) ++ f([a, b], 2) * c ++ f([a, b], 1) * c^2 ++ [c^3] $$
To handle sparsity, if c is zero, we can skip all monomials that contain it. We remember the current index and increment it properly for sparse input.
 Annotations
 @Since( "1.6.0" )

object
QuantileDiscretizer extends DefaultParamsReadable[QuantileDiscretizer] with Logging with Serializable
 Annotations
 @Since( "1.6.0" )

object
RFormula extends DefaultParamsReadable[RFormula] with Serializable
 Annotations
 @Since( "2.0.0" )

object
RFormulaModel extends MLReadable[RFormulaModel] with Serializable
 Annotations
 @Since( "2.0.0" )

object
RegexTokenizer extends DefaultParamsReadable[RegexTokenizer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
RobustScaler extends DefaultParamsReadable[RobustScaler] with Serializable
 Annotations
 @Since( "3.0.0" )

object
RobustScalerModel extends MLReadable[RobustScalerModel] with Serializable
 Annotations
 @Since( "3.0.0" )

object
SQLTransformer extends DefaultParamsReadable[SQLTransformer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
StandardScaler extends DefaultParamsReadable[StandardScaler] with Serializable
 Annotations
 @Since( "1.6.0" )

object
StandardScalerModel extends MLReadable[StandardScalerModel] with Serializable
 Annotations
 @Since( "1.6.0" )

object
StopWordsRemover extends DefaultParamsReadable[StopWordsRemover] with Serializable
 Annotations
 @Since( "1.6.0" )

object
StringIndexer extends DefaultParamsReadable[StringIndexer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
StringIndexerModel extends MLReadable[StringIndexerModel] with Serializable
 Annotations
 @Since( "1.6.0" )

object
Tokenizer extends DefaultParamsReadable[Tokenizer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
UnivariateFeatureSelector extends DefaultParamsReadable[UnivariateFeatureSelector] with Serializable
 Annotations
 @Since( "3.1.1" )

object
UnivariateFeatureSelectorModel extends MLReadable[UnivariateFeatureSelectorModel] with Serializable
 Annotations
 @Since( "3.1.1" )

object
VarianceThresholdSelector extends DefaultParamsReadable[VarianceThresholdSelector] with Serializable
 Annotations
 @Since( "3.1.0" )

object
VarianceThresholdSelectorModel extends MLReadable[VarianceThresholdSelectorModel] with Serializable
 Annotations
 @Since( "3.1.0" )

object
VectorAssembler extends DefaultParamsReadable[VectorAssembler] with Serializable
 Annotations
 @Since( "1.6.0" )

object
VectorIndexer extends DefaultParamsReadable[VectorIndexer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
VectorIndexerModel extends MLReadable[VectorIndexerModel] with Serializable
 Annotations
 @Since( "1.6.0" )

object
VectorSizeHint extends DefaultParamsReadable[VectorSizeHint] with Serializable
 Annotations
 @Since( "2.3.0" )

object
VectorSlicer extends DefaultParamsReadable[VectorSlicer] with Serializable
 Annotations
 @Since( "1.6.0" )

object
Word2Vec extends DefaultParamsReadable[Word2Vec] with Serializable
 Annotations
 @Since( "1.6.0" )

object
Word2VecModel extends MLReadable[Word2VecModel] with Serializable
 Annotations
 @Since( "1.6.0" )