Source code for pyspark.mllib.feature

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Python package for feature in MLlib.
from __future__ import absolute_import

import sys
import warnings
import random

from py4j.protocol import Py4JJavaError

from pyspark import RDD, SparkContext
from pyspark.mllib.common import callMLlibFunc, JavaModelWrapper
from pyspark.mllib.linalg import Vectors, Vector, _convert_to_vector

__all__ = ['Normalizer', 'StandardScalerModel', 'StandardScaler',
           'HashingTF', 'IDFModel', 'IDF', 'Word2Vec', 'Word2VecModel']

class VectorTransformer(object):
    .. note:: DeveloperApi

    Base class for transformation of a vector or RDD of vector
    def transform(self, vector):
        Applies transformation on a vector.

        :param vector: vector to be transformed.
        raise NotImplementedError

[docs]class Normalizer(VectorTransformer): """ .. note:: Experimental Normalizes samples individually to unit L\ :sup:`p`\ norm For any 1 <= `p` < float('inf'), normalizes samples using sum(abs(vector) :sup:`p`) :sup:`(1/p)` as norm. For `p` = float('inf'), max(abs(vector)) will be used as norm for normalization. >>> v = Vectors.dense(range(3)) >>> nor = Normalizer(1) >>> nor.transform(v) DenseVector([0.0, 0.3333, 0.6667]) >>> rdd = sc.parallelize([v]) >>> nor.transform(rdd).collect() [DenseVector([0.0, 0.3333, 0.6667])] >>> nor2 = Normalizer(float("inf")) >>> nor2.transform(v) DenseVector([0.0, 0.5, 1.0]) """ def __init__(self, p=2.0): """ :param p: Normalization in L^p^ space, p = 2 by default. """ assert p >= 1.0, "p should be greater than 1.0" self.p = float(p)
[docs] def transform(self, vector): """ Applies unit length normalization on a vector. :param vector: vector or RDD of vector to be normalized. :return: normalized vector. If the norm of the input is zero, it will return the input vector. """ sc = SparkContext._active_spark_context assert sc is not None, "SparkContext should be initialized first" if isinstance(vector, RDD): vector = else: vector = _convert_to_vector(vector) return callMLlibFunc("normalizeVector", self.p, vector)
class JavaVectorTransformer(JavaModelWrapper, VectorTransformer): """ Wrapper for the model in JVM """ def transform(self, vector): if isinstance(vector, RDD): vector = else: vector = _convert_to_vector(vector) return"transform", vector)
[docs]class StandardScalerModel(JavaVectorTransformer): """ .. note:: Experimental Represents a StandardScaler model that can transform vectors. """
[docs] def transform(self, vector): """ Applies standardization transformation on a vector. Note: In Python, transform cannot currently be used within an RDD transformation or action. Call transform directly on the RDD instead. :param vector: Vector or RDD of Vector to be standardized. :return: Standardized vector. If the variance of a column is zero, it will return default `0.0` for the column with zero variance. """ return JavaVectorTransformer.transform(self, vector)
[docs]class StandardScaler(object): """ .. note:: Experimental Standardizes features by removing the mean and scaling to unit variance using column summary statistics on the samples in the training set. >>> vs = [Vectors.dense([-2.0, 2.3, 0]), Vectors.dense([3.8, 0.0, 1.9])] >>> dataset = sc.parallelize(vs) >>> standardizer = StandardScaler(True, True) >>> model = >>> result = model.transform(dataset) >>> for r in result.collect(): r DenseVector([-0.7071, 0.7071, -0.7071]) DenseVector([0.7071, -0.7071, 0.7071]) """ def __init__(self, withMean=False, withStd=True): """ :param withMean: False by default. Centers the data with mean before scaling. It will build a dense output, so this does not work on sparse input and will raise an exception. :param withStd: True by default. Scales the data to unit standard deviation. """ if not (withMean or withStd): warnings.warn("Both withMean and withStd are false. The model does nothing.") self.withMean = withMean self.withStd = withStd
[docs] def fit(self, dataset): """ Computes the mean and variance and stores as a model to be used for later scaling. :param data: The data used to compute the mean and variance to build the transformation model. :return: a StandardScalarModel """ dataset = jmodel = callMLlibFunc("fitStandardScaler", self.withMean, self.withStd, dataset) return StandardScalerModel(jmodel)
[docs]class HashingTF(object): """ .. note:: Experimental Maps a sequence of terms to their term frequencies using the hashing trick. Note: the terms must be hashable (can not be dict/set/list...). >>> htf = HashingTF(100) >>> doc = "a a b b c d".split(" ") >>> htf.transform(doc) SparseVector(100, {1: 1.0, 14: 1.0, 31: 2.0, 44: 2.0}) """ def __init__(self, numFeatures=1 << 20): """ :param numFeatures: number of features (default: 2^20) """ self.numFeatures = numFeatures
[docs] def indexOf(self, term): """ Returns the index of the input term. """ return hash(term) % self.numFeatures
[docs] def transform(self, document): """ Transforms the input document (list of terms) to term frequency vectors, or transform the RDD of document to RDD of term frequency vectors. """ if isinstance(document, RDD): return freq = {} for term in document: i = self.indexOf(term) freq[i] = freq.get(i, 0) + 1.0 return Vectors.sparse(self.numFeatures, freq.items())
[docs]class IDFModel(JavaVectorTransformer): """ Represents an IDF model that can transform term frequency vectors. """
[docs] def transform(self, x): """ Transforms term frequency (TF) vectors to TF-IDF vectors. If `minDocFreq` was set for the IDF calculation, the terms which occur in fewer than `minDocFreq` documents will have an entry of 0. Note: In Python, transform cannot currently be used within an RDD transformation or action. Call transform directly on the RDD instead. :param x: an RDD of term frequency vectors or a term frequency vector :return: an RDD of TF-IDF vectors or a TF-IDF vector """ if isinstance(x, RDD): return JavaVectorTransformer.transform(self, x) x = _convert_to_vector(x) return JavaVectorTransformer.transform(self, x)
[docs]class IDF(object): """ .. note:: Experimental Inverse document frequency (IDF). The standard formulation is used: `idf = log((m + 1) / (d(t) + 1))`, where `m` is the total number of documents and `d(t)` is the number of documents that contain term `t`. This implementation supports filtering out terms which do not appear in a minimum number of documents (controlled by the variable `minDocFreq`). For terms that are not in at least `minDocFreq` documents, the IDF is found as 0, resulting in TF-IDFs of 0. >>> n = 4 >>> freqs = [Vectors.sparse(n, (1, 3), (1.0, 2.0)), ... Vectors.dense([0.0, 1.0, 2.0, 3.0]), ... Vectors.sparse(n, [1], [1.0])] >>> data = sc.parallelize(freqs) >>> idf = IDF() >>> model = >>> tfidf = model.transform(data) >>> for r in tfidf.collect(): r SparseVector(4, {1: 0.0, 3: 0.5754}) DenseVector([0.0, 0.0, 1.3863, 0.863]) SparseVector(4, {1: 0.0}) >>> model.transform(Vectors.dense([0.0, 1.0, 2.0, 3.0])) DenseVector([0.0, 0.0, 1.3863, 0.863]) >>> model.transform([0.0, 1.0, 2.0, 3.0]) DenseVector([0.0, 0.0, 1.3863, 0.863]) >>> model.transform(Vectors.sparse(n, (1, 3), (1.0, 2.0))) SparseVector(4, {1: 0.0, 3: 0.5754}) """ def __init__(self, minDocFreq=0): """ :param minDocFreq: minimum of documents in which a term should appear for filtering """ self.minDocFreq = minDocFreq
[docs] def fit(self, dataset): """ Computes the inverse document frequency. :param dataset: an RDD of term frequency vectors """ if not isinstance(dataset, RDD): raise TypeError("dataset should be an RDD of term frequency vectors") jmodel = callMLlibFunc("fitIDF", self.minDocFreq, return IDFModel(jmodel)
[docs]class Word2VecModel(JavaVectorTransformer): """ class for Word2Vec model """
[docs] def transform(self, word): """ Transforms a word to its vector representation Note: local use only :param word: a word :return: vector representation of word(s) """ try: return"transform", word) except Py4JJavaError: raise ValueError("%s not found" % word)
[docs] def findSynonyms(self, word, num): """ Find synonyms of a word :param word: a word or a vector representation of word :param num: number of synonyms to find :return: array of (word, cosineSimilarity) Note: local use only """ if not isinstance(word, basestring): word = _convert_to_vector(word) words, similarity ="findSynonyms", word, num) return zip(words, similarity)
[docs]class Word2Vec(object): """ Word2Vec creates vector representation of words in a text corpus. The algorithm first constructs a vocabulary from the corpus and then learns vector representation of words in the vocabulary. The vector representation can be used as features in natural language processing and machine learning algorithms. We used skip-gram model in our implementation and hierarchical softmax method to train the model. The variable names in the implementation matches the original C implementation. For original C implementation, see For research papers, see Efficient Estimation of Word Representations in Vector Space and Distributed Representations of Words and Phrases and their Compositionality. >>> sentence = "a b " * 100 + "a c " * 10 >>> localDoc = [sentence, sentence] >>> doc = sc.parallelize(localDoc).map(lambda line: line.split(" ")) >>> model = Word2Vec().setVectorSize(10).setSeed(42L).fit(doc) >>> syms = model.findSynonyms("a", 2) >>> [s[0] for s in syms] [u'b', u'c'] >>> vec = model.transform("a") >>> syms = model.findSynonyms(vec, 2) >>> [s[0] for s in syms] [u'b', u'c'] """ def __init__(self): """ Construct Word2Vec instance """ self.vectorSize = 100 self.learningRate = 0.025 self.numPartitions = 1 self.numIterations = 1 self.seed = random.randint(0, sys.maxint)
[docs] def setVectorSize(self, vectorSize): """ Sets vector size (default: 100). """ self.vectorSize = vectorSize return self
[docs] def setLearningRate(self, learningRate): """ Sets initial learning rate (default: 0.025). """ self.learningRate = learningRate return self
[docs] def setNumPartitions(self, numPartitions): """ Sets number of partitions (default: 1). Use a small number for accuracy. """ self.numPartitions = numPartitions return self
[docs] def setNumIterations(self, numIterations): """ Sets number of iterations (default: 1), which should be smaller than or equal to number of partitions. """ self.numIterations = numIterations return self
[docs] def setSeed(self, seed): """ Sets random seed. """ self.seed = seed return self
[docs] def fit(self, data): """ Computes the vector representation of each word in vocabulary. :param data: training data. RDD of list of string :return: Word2VecModel instance """ if not isinstance(data, RDD): raise TypeError("data should be an RDD of list of string") jmodel = callMLlibFunc("trainWord2Vec", data, int(self.vectorSize), float(self.learningRate), int(self.numPartitions), int(self.numIterations), long(self.seed)) return Word2VecModel(jmodel)
def _test(): import doctest from pyspark import SparkContext globs = globals().copy() globs['sc'] = SparkContext('local[4]', 'PythonTest', batchSize=2) (failure_count, test_count) = doctest.testmod(globs=globs, optionflags=doctest.ELLIPSIS) globs['sc'].stop() if failure_count: exit(-1) if __name__ == "__main__": sys.path.pop(0) _test()