[SPARK-29808][ML][PYTHON] StopWordsRemover should support multi-cols

### What changes were proposed in this pull request?
Add multi-cols support in StopWordsRemover

### Why are the changes needed?
As a basic Transformer, StopWordsRemover should support multi-cols.
Param stopWords can be applied across all columns.

### Does this PR introduce any user-facing change?
```StopWordsRemover.setInputCols```
```StopWordsRemover.setOutputCols```

### How was this patch tested?
Unit tests

Closes apache#26480 from huaxingao/spark-29808.

Authored-by: Huaxin Gao <[email protected]>
Signed-off-by: Sean Owen <[email protected]>

Author: huaxingao

mllib/src/main/scala/org/apache/spark/ml/feature/StopWordsRemover.scala

@@ -22,23 +22,28 @@ import java.util.Locale
 import org.apache.spark.annotation.Since
 import org.apache.spark.ml.Transformer
 import org.apache.spark.ml.param._
-import org.apache.spark.ml.param.shared.{HasInputCol, HasOutputCol}
+import org.apache.spark.ml.param.shared.{HasInputCol, HasInputCols, HasOutputCol, HasOutputCols}
 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}
+import org.apache.spark.sql.types.{ArrayType, StringType, StructField, StructType}
 
 /**
  * A feature transformer that filters out stop words from input.
  *
+ * Since 3.0.0, `StopWordsRemover` can filter out multiple columns at once by setting the
+ * `inputCols` parameter. Note that when both the `inputCol` and `inputCols` parameters are set,
+ * an Exception will be thrown.
+ *
  * @note null values from input array are preserved unless adding null to stopWords
  * explicitly.
  *
  * @see <a href="http://en.wikipedia.org/wiki/Stop_words">Stop words (Wikipedia)</a>
  */
 @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 {
+  extends Transformer with HasInputCol with HasOutputCol with HasInputCols with HasOutputCols
+    with DefaultParamsWritable {
 
   @Since("1.5.0")
   def this() = this(Identifiable.randomUID("stopWords"))
@@ -51,6 +56,14 @@ class StopWordsRemover @Since("1.5.0") (@Since("1.5.0") override val uid: String
   @Since("1.5.0")
   def setOutputCol(value: String): this.type = set(outputCol, value)
 
+  /** @group setParam */
+  @Since("3.0.0")
+  def setInputCols(value: Array[String]): this.type = set(inputCols, value)
+
+  /** @group setParam */
+  @Since("3.0.0")
+  def setOutputCols(value: Array[String]): this.type = set(outputCols, value)
+
   /**
    * The words to be filtered out.
    * Default: English stop words
@@ -121,6 +134,15 @@ class StopWordsRemover @Since("1.5.0") (@Since("1.5.0") override val uid: String
     }
   }
 
+  /** Returns the input and output column names corresponding in pair. */
+  private[feature] def getInOutCols(): (Array[String], Array[String]) = {
+    if (isSet(inputCol)) {
+      (Array($(inputCol)), Array($(outputCol)))
+    } else {
+      ($(inputCols), $(outputCols))
+    }
+  }
+
   setDefault(stopWords -> StopWordsRemover.loadDefaultStopWords("english"),
     caseSensitive -> false, locale -> getDefaultOrUS.toString)
 
@@ -142,16 +164,38 @@ class StopWordsRemover @Since("1.5.0") (@Since("1.5.0") override val uid: String
         terms.filter(s => !lowerStopWords.contains(toLower(s)))
       }
     }
-    val metadata = outputSchema($(outputCol)).metadata
-    dataset.select(col("*"), t(col($(inputCol))).as($(outputCol), metadata))
+
+    val (inputColNames, outputColNames) = getInOutCols()
+    val ouputCols = inputColNames.map { inputColName =>
+      t(col(inputColName))
+    }
+    val ouputMetadata = outputColNames.map(outputSchema(_).metadata)
+    dataset.withColumns(outputColNames, ouputCols, ouputMetadata)
   }
 
   @Since("1.5.0")
   override def transformSchema(schema: StructType): StructType = {
-    val inputType = schema($(inputCol)).dataType
-    require(inputType.sameType(ArrayType(StringType)), "Input type must be " +
-      s"${ArrayType(StringType).catalogString} but got ${inputType.catalogString}.")
-    SchemaUtils.appendColumn(schema, $(outputCol), inputType, schema($(inputCol)).nullable)
+    ParamValidators.checkSingleVsMultiColumnParams(this, Seq(outputCol),
+      Seq(outputCols))
+
+    if (isSet(inputCols)) {
+      require(getInputCols.length == getOutputCols.length,
+        s"StopWordsRemover $this has mismatched Params " +
+          s"for multi-column transform. Params ($inputCols, $outputCols) should have " +
+          "equal lengths, but they have different lengths: " +
+          s"(${getInputCols.length}, ${getOutputCols.length}).")
+    }
+
+    val (inputColNames, outputColNames) = getInOutCols()
+    val newCols = inputColNames.zip(outputColNames).map { case (inputColName, outputColName) =>
+       require(!schema.fieldNames.contains(outputColName),
+        s"Output Column $outputColName already exists.")
+      val inputType = schema(inputColName).dataType
+      require(inputType.sameType(ArrayType(StringType)), "Input type must be " +
+        s"${ArrayType(StringType).catalogString} but got ${inputType.catalogString}.")
+      StructField(outputColName, inputType, schema(inputColName).nullable)
+    }
+    StructType(schema.fields ++ newCols)
   }
 
   @Since("1.5.0")

mllib/src/test/scala/org/apache/spark/ml/feature/StopWordsRemoverSuite.scala

@@ -19,6 +19,7 @@ package org.apache.spark.ml.feature
 
 import java.util.Locale
 
+import org.apache.spark.ml.Pipeline
 import org.apache.spark.ml.util.{DefaultReadWriteTest, MLTest}
 import org.apache.spark.sql.{DataFrame, Row}
 
@@ -181,12 +182,19 @@ class StopWordsRemoverSuite extends MLTest with DefaultReadWriteTest {
   }
 
   test("read/write") {
-    val t = new StopWordsRemover()
+    val t1 = new StopWordsRemover()
       .setInputCol("myInputCol")
       .setOutputCol("myOutputCol")
       .setStopWords(Array("the", "a"))
       .setCaseSensitive(true)
-    testDefaultReadWrite(t)
+    testDefaultReadWrite(t1)
+
+    val t2 = new StopWordsRemover()
+      .setInputCols(Array("input1", "input2", "input3"))
+      .setOutputCols(Array("result1", "result2", "result3"))
+      .setStopWords(Array("the", "a"))
+      .setCaseSensitive(true)
+    testDefaultReadWrite(t2)
   }
 
   test("StopWordsRemover output column already exists") {
@@ -199,7 +207,7 @@ class StopWordsRemoverSuite extends MLTest with DefaultReadWriteTest {
     testTransformerByInterceptingException[(Array[String], Array[String])](
       dataSet,
       remover,
-      s"requirement failed: Column $outputCol already exists.",
+      s"requirement failed: Output Column $outputCol already exists.",
       "expected")
   }
 
@@ -217,4 +225,123 @@ class StopWordsRemoverSuite extends MLTest with DefaultReadWriteTest {
       Locale.setDefault(oldDefault)
     }
   }
+
+  test("Multiple Columns: StopWordsRemover default") {
+    val remover = new StopWordsRemover()
+      .setInputCols(Array("raw1", "raw2"))
+      .setOutputCols(Array("filtered1", "filtered2"))
+    val df = Seq(
+      (Seq("test", "test"), Seq("test1", "test2"), Seq("test", "test"), Seq("test1", "test2")),
+      (Seq("a", "b", "c", "d"), Seq("a", "b"), Seq("b", "c", "d"), Seq("b")),
+      (Seq("a", "the", "an"), Seq("the", "an"), Seq(), Seq()),
+      (Seq("A", "The", "AN"), Seq("A", "The"), Seq(), Seq()),
+      (Seq(null), Seq(null), Seq(null), Seq(null)),
+      (Seq(), Seq(), Seq(), Seq())
+    ).toDF("raw1", "raw2", "expected1", "expected2")
+
+    remover.transform(df)
+      .select("filtered1", "expected1", "filtered2", "expected2")
+      .collect().foreach {
+        case Row(r1: Seq[String], e1: Seq[String], r2: Seq[String], e2: Seq[String]) =>
+          assert(r1 === e1,
+            s"The result value is not correct after bucketing. Expected $e1 but found $r1")
+          assert(r2 === e2,
+            s"The result value is not correct after bucketing. Expected $e2 but found $r2")
+    }
+  }
+
+  test("Multiple Columns: StopWordsRemover with particular stop words list") {
+    val stopWords = Array("test", "a", "an", "the")
+    val remover = new StopWordsRemover()
+      .setInputCols(Array("raw1", "raw2"))
+      .setOutputCols(Array("filtered1", "filtered2"))
+      .setStopWords(stopWords)
+    val df = Seq(
+      (Seq("test", "test"), Seq("test1", "test2"), Seq(), Seq("test1", "test2")),
+      (Seq("a", "b", "c", "d"), Seq("a", "b"), Seq("b", "c", "d"), Seq("b")),
+      (Seq("a", "the", "an"), Seq("a", "the", "test1"), Seq(), Seq("test1")),
+      (Seq("A", "The", "AN"), Seq("A", "The", "AN"), Seq(), Seq()),
+      (Seq(null), Seq(null), Seq(null), Seq(null)),
+      (Seq(), Seq(), Seq(), Seq())
+    ).toDF("raw1", "raw2", "expected1", "expected2")
+
+    remover.transform(df)
+      .select("filtered1", "expected1", "filtered2", "expected2")
+      .collect().foreach {
+        case Row(r1: Seq[String], e1: Seq[String], r2: Seq[String], e2: Seq[String]) =>
+          assert(r1 === e1,
+            s"The result value is not correct after bucketing. Expected $e1 but found $r1")
+          assert(r2 === e2,
+            s"The result value is not correct after bucketing. Expected $e2 but found $r2")
+    }
+  }
+
+  test("Compare single/multiple column(s) StopWordsRemover in pipeline") {
+    val df = Seq(
+      (Seq("test", "test"), Seq("test1", "test2")),
+      (Seq("a", "b", "c", "d"), Seq("a", "b")),
+      (Seq("a", "the", "an"), Seq("a", "the", "test1")),
+      (Seq("A", "The", "AN"), Seq("A", "The", "AN")),
+      (Seq(null), Seq(null)),
+      (Seq(), Seq())
+    ).toDF("input1", "input2")
+
+    val multiColsRemover = new StopWordsRemover()
+      .setInputCols(Array("input1", "input2"))
+      .setOutputCols(Array("output1", "output2"))
+
+    val plForMultiCols = new Pipeline()
+      .setStages(Array(multiColsRemover))
+      .fit(df)
+
+    val removerForCol1 = new StopWordsRemover()
+      .setInputCol("input1")
+      .setOutputCol("output1")
+    val removerForCol2 = new StopWordsRemover()
+      .setInputCol("input2")
+      .setOutputCol("output2")
+
+    val plForSingleCol = new Pipeline()
+      .setStages(Array(removerForCol1, removerForCol2))
+      .fit(df)
+
+    val resultForSingleCol = plForSingleCol.transform(df)
+      .select("output1", "output2")
+      .collect()
+    val resultForMultiCols = plForMultiCols.transform(df)
+      .select("output1", "output2")
+      .collect()
+
+    resultForSingleCol.zip(resultForMultiCols).foreach {
+      case (rowForSingle, rowForMultiCols) =>
+        assert(rowForSingle === rowForMultiCols)
+    }
+  }
+
+  test("Multiple Columns: Mismatched sizes of inputCols/outputCols") {
+    val remover = new StopWordsRemover()
+      .setInputCols(Array("input1"))
+      .setOutputCols(Array("result1", "result2"))
+    val df = Seq(
+      (Seq("A"), Seq("A")),
+      (Seq("The", "the"), Seq("The"))
+    ).toDF("input1", "input2")
+    intercept[IllegalArgumentException] {
+      remover.transform(df).count()
+    }
+  }
+
+  test("Multiple Columns: Set both of inputCol/inputCols") {
+    val remover = new StopWordsRemover()
+      .setInputCols(Array("input1", "input2"))
+      .setOutputCols(Array("result1", "result2"))
+      .setInputCol("input1")
+    val df = Seq(
+      (Seq("A"), Seq("A")),
+      (Seq("The", "the"), Seq("The"))
+    ).toDF("input1", "input2")
+    intercept[IllegalArgumentException] {
+      remover.transform(df).count()
+    }
+  }
 }

python/pyspark/ml/feature.py

@@ -3774,9 +3774,13 @@ def setOutputCol(self, value):
         return self._set(outputCol=value)
 
 
-class StopWordsRemover(JavaTransformer, HasInputCol, HasOutputCol, JavaMLReadable, JavaMLWritable):
+class StopWordsRemover(JavaTransformer, HasInputCol, HasOutputCol, HasInputCols, HasOutputCols,
+                       JavaMLReadable, JavaMLWritable):
     """
     A feature transformer that filters out stop words from input.
+    Since 3.0.0, :py:class:`StopWordsRemover` can filter out multiple columns at once by setting
+    the :py:attr:`inputCols` parameter. Note that when both the :py:attr:`inputCol` and
+    :py:attr:`inputCols` parameters are set, an Exception will be thrown.
 
     .. note:: null values from input array are preserved unless adding null to stopWords explicitly.
 
@@ -3795,6 +3799,17 @@ class StopWordsRemover(JavaTransformer, HasInputCol, HasOutputCol, JavaMLReadabl
     True
     >>> loadedRemover.getCaseSensitive() == remover.getCaseSensitive()
     True
+    >>> df2 = spark.createDataFrame([(["a", "b", "c"], ["a", "b"])], ["text1", "text2"])
+    >>> remover2 = StopWordsRemover(stopWords=["b"])
+    >>> remover2.setInputCols(["text1", "text2"]).setOutputCols(["words1", "words2"])
+    StopWordsRemover...
+    >>> remover2.transform(df2).show()
+    +---------+------+------+------+
+    |    text1| text2|words1|words2|
+    +---------+------+------+------+
+    |[a, b, c]|[a, b]|[a, c]|   [a]|
+    +---------+------+------+------+
+    ...
 
     .. versionadded:: 1.6.0
     """
@@ -3808,10 +3823,10 @@ class StopWordsRemover(JavaTransformer, HasInputCol, HasOutputCol, JavaMLReadabl
 
     @keyword_only
     def __init__(self, inputCol=None, outputCol=None, stopWords=None, caseSensitive=False,
-                 locale=None):
+                 locale=None, inputCols=None, outputCols=None):
         """
         __init__(self, inputCol=None, outputCol=None, stopWords=None, caseSensitive=false, \
-        locale=None)
+                 locale=None, inputCols=None, outputCols=None)
         """
         super(StopWordsRemover, self).__init__()
         self._java_obj = self._new_java_obj("org.apache.spark.ml.feature.StopWordsRemover",
@@ -3824,10 +3839,10 @@ def __init__(self, inputCol=None, outputCol=None, stopWords=None, caseSensitive=
     @keyword_only
     @since("1.6.0")
     def setParams(self, inputCol=None, outputCol=None, stopWords=None, caseSensitive=False,
-                  locale=None):
+                  locale=None, inputCols=None, outputCols=None):
         """
         setParams(self, inputCol=None, outputCol=None, stopWords=None, caseSensitive=false, \
-        locale=None)
+                  locale=None, inputCols=None, outputCols=None)
         Sets params for this StopWordRemover.
         """
         kwargs = self._input_kwargs
@@ -3887,6 +3902,20 @@ def setOutputCol(self, value):
         """
         return self._set(outputCol=value)
 
+    @since("3.0.0")
+    def setInputCols(self, value):
+        """
+        Sets the value of :py:attr:`inputCols`.
+        """
+        return self._set(inputCols=value)
+
+    @since("3.0.0")
+    def setOutputCols(self, value):
+        """
+        Sets the value of :py:attr:`outputCols`.
+        """
+        return self._set(outputCols=value)
+
     @staticmethod
     @since("2.0.0")
     def loadDefaultStopWords(language):