Github user jkbradley commented on a diff in the pull request:
https://github.com/apache/spark/pull/6894#discussion_r33078047
--- Diff:
mllib/src/main/scala/org/apache/spark/ml/feature/DiscreteCosineTransformer.scala
---
@@ -0,0 +1,88 @@
+/*
+ * 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 edu.emory.mathcs.jtransforms.dct._
+
+import org.apache.spark.annotation.Experimental
+import org.apache.spark.ml.UnaryTransformer
+import org.apache.spark.ml.param.BooleanParam
+import org.apache.spark.ml.util.Identifiable
+import org.apache.spark.sql.types.{NumericType, ArrayType, DataType,
DoubleType}
+
+/**
+ * :: Experimental ::
+ * A feature transformer that takes the 1D discrete cosine transform of a
real vector.
+ * It returns a real vector of the same length representing the DCT. The
return vector is scaled
+ * such that the transform matrix is unitary.
+ *
+ * More information:
https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-II
+ */
+@Experimental
+// TODO: explore variance -IN (and +OUT in UnaryTransformer)
--- End diff --
What does this mean? If this is a note-to-self, I'd remove it for the PR.
If it's a real to-do item, I'd make a follow-up JIRA and note the JIRA number
here.
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