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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.spark.ml.feature
import org.apache.spark.annotation.{Experimental, Since}
import org.apache.spark.ml.Transformer
import org.apache.spark.ml.param.{BooleanParam, ParamMap, StringArrayParam}
import org.apache.spark.ml.param.shared.{HasInputCol, HasOutputCol}
import org.apache.spark.ml.util._
import org.apache.spark.sql.{DataFrame, Dataset}
import org.apache.spark.sql.functions.{col, udf}
import org.apache.spark.sql.types.{ArrayType, StringType, StructType}
/**
* :: Experimental ::
* A feature transformer that filters out stop words from input.
* Note: null values from input array are preserved unless adding null to stopWords explicitly.
* @see [[http://en.wikipedia.org/wiki/Stop_words]]
*/
@Experimental
@Since("1.5.0")
class StopWordsRemover @Since("1.5.0") (@Since("1.5.0") override val uid: String)
extends Transformer with HasInputCol with HasOutputCol with DefaultParamsWritable {
@Since("1.5.0")
def this() = this(Identifiable.randomUID("stopWords"))
/** @group setParam */
@Since("1.5.0")
def setInputCol(value: String): this.type = set(inputCol, value)
/** @group setParam */
@Since("1.5.0")
def setOutputCol(value: String): this.type = set(outputCol, value)
/**
* The words to be filtered out.
* Default: English stop words
* @see [[StopWordsRemover.loadDefaultStopWords()]]
* @group param
*/
@Since("1.5.0")
val stopWords: StringArrayParam =
new StringArrayParam(this, "stopWords", "the words to be filtered out")
/** @group setParam */
@Since("1.5.0")
def setStopWords(value: Array[String]): this.type = set(stopWords, value)
/** @group getParam */
@Since("1.5.0")
def getStopWords: Array[String] = $(stopWords)
/**
* Whether to do a case sensitive comparison over the stop words.
* Default: false
* @group param
*/
@Since("1.5.0")
val caseSensitive: BooleanParam = new BooleanParam(this, "caseSensitive",
"whether to do a case-sensitive comparison over the stop words")
/** @group setParam */
@Since("1.5.0")
def setCaseSensitive(value: Boolean): this.type = set(caseSensitive, value)
/** @group getParam */
@Since("1.5.0")
def getCaseSensitive: Boolean = $(caseSensitive)
setDefault(stopWords -> StopWordsRemover.loadDefaultStopWords("english"), caseSensitive -> false)
@Since("2.0.0")
override def transform(dataset: Dataset[_]): DataFrame = {
val outputSchema = transformSchema(dataset.schema)
val t = if ($(caseSensitive)) {
val stopWordsSet = $(stopWords).toSet
udf { terms: Seq[String] =>
terms.filter(s => !stopWordsSet.contains(s))
}
} else {
// TODO: support user locale (SPARK-15064)
val toLower = (s: String) => if (s != null) s.toLowerCase else s
val lowerStopWords = $(stopWords).map(toLower(_)).toSet
udf { terms: Seq[String] =>
terms.filter(s => !lowerStopWords.contains(toLower(s)))
}
}
val metadata = outputSchema($(outputCol)).metadata
dataset.select(col("*"), t(col($(inputCol))).as($(outputCol), metadata))
}
@Since("1.5.0")
override def transformSchema(schema: StructType): StructType = {
val inputType = schema($(inputCol)).dataType
require(inputType.sameType(ArrayType(StringType)),
s"Input type must be ArrayType(StringType) but got $inputType.")
SchemaUtils.appendColumn(schema, $(outputCol), inputType, schema($(inputCol)).nullable)
}
@Since("1.5.0")
override def copy(extra: ParamMap): StopWordsRemover = defaultCopy(extra)
}
@Since("1.6.0")
object StopWordsRemover extends DefaultParamsReadable[StopWordsRemover] {
private[feature]
val supportedLanguages = Set("danish", "dutch", "english", "finnish", "french", "german",
"hungarian", "italian", "norwegian", "portuguese", "russian", "spanish", "swedish", "turkish")
@Since("1.6.0")
override def load(path: String): StopWordsRemover = super.load(path)
/**
* Loads the default stop words for the given language.
* Supported languages: danish, dutch, english, finnish, french, german, hungarian,
* italian, norwegian, portuguese, russian, spanish, swedish, turkish
* @see [[http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/snowball/stopwords/]]
*/
@Since("2.0.0")
def loadDefaultStopWords(language: String): Array[String] = {
require(supportedLanguages.contains(language),
s"$language is not in the supported language list: ${supportedLanguages.mkString(", ")}.")
val is = getClass.getResourceAsStream(s"/org/apache/spark/ml/feature/stopwords/$language.txt")
scala.io.Source.fromInputStream(is)(scala.io.Codec.UTF8).getLines().toArray
}
}
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