[SPARK-7651] [MLLIB] [PYSPARK] GMM predict, predictSoft should raise error on bad input

In the Python API for Gaussian Mixture Model, predict() and predictSoft() methods should raise an error when the input argument is not an RDD.

Author: FlytxtRnD <meethu.mathew@flytxt.com>

Closes #6180 from FlytxtRnD/GmmPredictException and squashes the following commits:

4b6aa11 [FlytxtRnD] Raise error if the input to predict()/predictSoft() is not an RDD

python/pyspark/mllib/clustering.py

@@ -212,6 +212,9 @@ class GaussianMixtureModel(object):
         if isinstance(x, RDD):
             cluster_labels = self.predictSoft(x).map(lambda z: z.index(max(z)))
             return cluster_labels
+        else:
+            raise TypeError("x should be represented by an RDD, "
+                            "but got %s." % type(x))
 
     def predictSoft(self, x):
         """
@@ -225,6 +228,9 @@ class GaussianMixtureModel(object):
             membership_matrix = callMLlibFunc("predictSoftGMM", x.map(_convert_to_vector),
                                               _convert_to_vector(self._weights), means, sigmas)
             return membership_matrix.map(lambda x: pyarray.array('d', x))
+        else:
+            raise TypeError("x should be represented by an RDD, "
+                            "but got %s." % type(x))
 
 
 class GaussianMixture(object):