Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/8485#discussion_r38116030
--- Diff: python/pyspark/ml/feature.py ---
@@ -167,6 +167,65 @@ def getSplits(self):
@inherit_doc
+class DCT(JavaTransformer, HasInputCol, HasOutputCol):
+ """
+ A feature transformer that takes the 1D discrete cosine transform of a
real vector. No zero
+ padding is performed on the input 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 (aka scaled DCT-II).
+
+ More information on
`https://en.wikipedia.org/wiki/Discrete_cosine_transform#DCT-II Wikipedia`.
+
+ >>> from pyspark.mllib.linalg import Vectors
+ >>> df = sqlContext.createDataFrame([(Vectors.dense([5.0, 8.0,
6.0]),)], ["vec"])
+ >>> dct = DCT(inverse=False, inputCol="vec", outputCol="resultVec")
+ >>> dct.transform(df).head().resultVec
+ DenseVector([10.969..., -0.707..., -2.041...])
+ >>> dct.setInverse(True).transform(df).head().resultVec
--- End diff --
I would transform `resultVec` back to `origVec` to show that this is the
inverse.
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