[SPARK-9138] [MLLIB] fix Vectors.dense

Vectors.dense() should accept numbers directly, like the one in Scala. We already use it in doctests, it worked by luck.

cc mengxr jkbradley

Author: Davies Liu <davies@databricks.com>

Closes #7476 from davies/fix_vectors_dense and squashes the following commits:

e0fd292 [Davies Liu] fix Vectors.dense

python/pyspark/mllib/linalg.py

@@ -30,6 +30,7 @@ if sys.version >= '3':
     basestring = str
     xrange = range
     import copyreg as copy_reg
+    long = int
 else:
     from itertools import izip as zip
     import copy_reg
@@ -770,14 +771,18 @@ class Vectors(object):
         return SparseVector(size, *args)
 
     @staticmethod
-    def dense(elements):
+    def dense(*elements):
         """
-        Create a dense vector of 64-bit floats from a Python list. Always
-        returns a NumPy array.
+        Create a dense vector of 64-bit floats from a Python list or numbers.
 
         >>> Vectors.dense([1, 2, 3])
         DenseVector([1.0, 2.0, 3.0])
+        >>> Vectors.dense(1.0, 2.0)
+        DenseVector([1.0, 2.0])
         """
+        if len(elements) == 1 and not isinstance(elements[0], (float, int, long)):
+            # it's list, numpy.array or other iterable object.
+            elements = elements[0]
         return DenseVector(elements)
 
     @staticmethod