Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/19527#discussion_r158659167
--- Diff:
mllib/src/main/scala/org/apache/spark/ml/feature/OneHotEncoderEstimator.scala
---
@@ -0,0 +1,479 @@
+/*
+ * 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.hadoop.fs.Path
+
+import org.apache.spark.SparkException
+import org.apache.spark.annotation.Since
+import org.apache.spark.ml.{Estimator, Model}
+import org.apache.spark.ml.attribute._
+import org.apache.spark.ml.linalg.Vectors
+import org.apache.spark.ml.param._
+import org.apache.spark.ml.param.shared.{HasHandleInvalid, HasInputCols,
HasOutputCols}
+import org.apache.spark.ml.util._
+import org.apache.spark.sql.{DataFrame, Dataset}
+import org.apache.spark.sql.expressions.UserDefinedFunction
+import org.apache.spark.sql.functions.{col, lit, udf}
+import org.apache.spark.sql.types.{DoubleType, NumericType, StructField,
StructType}
+
+/** Private trait for params and common methods for OneHotEncoderEstimator
and OneHotEncoderModel */
+private[ml] trait OneHotEncoderBase extends Params with HasHandleInvalid
+ with HasInputCols with HasOutputCols {
+
+ /**
+ * Param for how to handle invalid data.
+ * Options are 'keep' (invalid data presented as an extra categorical
feature) or
+ * 'error' (throw an error).
+ * Default: "error"
+ * @group param
+ */
+ @Since("2.3.0")
+ override val handleInvalid: Param[String] = new Param[String](this,
"handleInvalid",
+ "How to handle invalid data " +
+ "Options are 'keep' (invalid data presented as an extra categorical
feature) " +
+ "or error (throw an error).",
+
ParamValidators.inArray(OneHotEncoderEstimator.supportedHandleInvalids))
+
+ setDefault(handleInvalid, OneHotEncoderEstimator.ERROR_INVALID)
+
+ /**
+ * Whether to drop the last category in the encoded vector (default:
true)
+ * @group param
+ */
+ @Since("2.3.0")
+ final val dropLast: BooleanParam =
+ new BooleanParam(this, "dropLast", "whether to drop the last category")
+ setDefault(dropLast -> true)
+
+ /** @group getParam */
+ @Since("2.3.0")
+ def getDropLast: Boolean = $(dropLast)
+
+ protected def validateAndTransformSchema(schema: StructType): StructType
= {
+ val inputColNames = $(inputCols)
+ val outputColNames = $(outputCols)
+ val existingFields = schema.fields
+
+ require(inputColNames.length == outputColNames.length,
+ s"The number of input columns ${inputColNames.length} must be the
same as the number of " +
+ s"output columns ${outputColNames.length}.")
+
+ inputColNames.zip(outputColNames).map { case (inputColName,
outputColName) =>
+ require(schema(inputColName).dataType.isInstanceOf[NumericType],
+ s"Input column must be of type NumericType but got
${schema(inputColName).dataType}")
+ require(!existingFields.exists(_.name == outputColName),
+ s"Output column $outputColName already exists.")
+ }
+
+ // Prepares output columns with proper attributes by examining input
columns.
+ val inputFields = $(inputCols).map(schema(_))
+ val keepInvalid = $(handleInvalid) ==
OneHotEncoderEstimator.KEEP_INVALID
+
+ val outputFields = inputFields.zip(outputColNames).map { case
(inputField, outputColName) =>
+ OneHotEncoderCommon.transformOutputColumnSchema(
+ inputField, $(dropLast), outputColName, keepInvalid)
+ }
+ StructType(schema.fields ++ outputFields)
+ }
+}
+
+/**
+ * A one-hot encoder that maps a column of category indices to a column of
binary vectors, with
+ * at most a single one-value 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 via
`dropLast`),
+ * 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]`.
+ *
+ * @note This is different from scikit-learn'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 when `dropLast` is true, invalid values are
encoded as all-zeros
+ * vector.
+ *
--- End diff --
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