com.microsoft.ml.spark.featurize.text.PageSplitter.scala Maven / Gradle / Ivy
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// Copyright (C) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License. See LICENSE in project root for information.
package com.microsoft.ml.spark.featurize.text
import com.microsoft.ml.spark.core.contracts.{HasInputCol, HasOutputCol, Wrappable}
import org.apache.spark.ml._
import org.apache.spark.ml.param._
import org.apache.spark.ml.util._
import org.apache.spark.sql.functions.{col, udf}
import org.apache.spark.sql.types._
import org.apache.spark.sql.{DataFrame, Dataset}
object PageSplitter extends DefaultParamsReadable[PageSplitter]
/** Splits text into chunks of at most n characters
*
* @param uid The id of the module
*/
class PageSplitter(override val uid: String)
extends Transformer with HasInputCol with HasOutputCol with Wrappable with DefaultParamsWritable {
def this() = this(Identifiable.randomUID("PageSplitter"))
setDefault(outputCol, uid + "_output")
val maximumPageLength =
new IntParam(this, "maximumPageLength",
"the maximum number of characters to be in a page")
def setMaximumPageLength(v: Int): this.type = set(maximumPageLength, v)
def getMaximumPageLength: Int = $(maximumPageLength)
val minimumPageLength =
new IntParam(this, "minimumPageLength",
"the the minimum number of characters " +
"to have on a page in order to preserve work boundaries")
def setMinimumPageLength(v: Int): this.type = set(minimumPageLength, v)
def getMinimumPageLength: Int = $(minimumPageLength)
val boundaryRegex = new Param[String](this, "boundaryRegex", "how to split into words")
def setBoundaryRegex(v: String): this.type = set(boundaryRegex, v)
def getBoundaryRegex: String = $(boundaryRegex)
setDefault(maximumPageLength -> 5000, minimumPageLength -> 4500, boundaryRegex -> "\\s")
def split(textOpt: String): Seq[String] = {
Option(textOpt).map { text =>
if (text.length < getMaximumPageLength) {
Seq(text)
} else {
val lengths = text
.split(getBoundaryRegex)
.map(_.length)
.flatMap(l => List(l, 1))
.dropRight(1)
val indicies = lengths.scanLeft((0, 0, Nil: List[Int])) { case ((total, count, _), l) =>
if (count + l < getMaximumPageLength) {
(total + l, count + l, Nil)
} else if (count > getMinimumPageLength) {
(total + l, l, List(total))
} else {
val firstPageChars = getMaximumPageLength - count
val firstPage = firstPageChars + total
val remainingChars = l - firstPageChars
val numPages = remainingChars / getMaximumPageLength
val remainder = remainingChars - getMaximumPageLength * numPages
val pages = List(firstPage) ::: (1 to numPages).map(i =>
total + firstPageChars + getMaximumPageLength * i).toList
(total + l, remainder, pages)
}
}.flatMap(_._3)
val words = (List(0) ::: indicies.toList ::: List(text.length))
.sliding(2)
.map { case List(start, end) => text.substring(start, end) }
.toSeq
words
}
}.orNull
}
override def transform(dataset: Dataset[_]): DataFrame = {
dataset.toDF().withColumn(getOutputCol, udf(split _, ArrayType(StringType))(col(getInputCol)))
}
override def copy(extra: ParamMap): MultiNGram =
defaultCopy(extra)
def transformSchema(schema: StructType): StructType = {
assert(schema(getInputCol).dataType == StringType)
schema.add(getOutputCol, ArrayType(StringType))
}
}