ENH Add MultiIndex.from_product convenience function

doc/source/indexing.rst

@@ -1539,8 +1539,9 @@ The ``MultiIndex`` object is the hierarchical analogue of the standard
 ``Index`` object which typically stores the axis labels in pandas objects. You
 can think of ``MultiIndex`` an array of tuples where each tuple is unique. A
 ``MultiIndex`` can be created from a list of arrays (using
-``MultiIndex.from_arrays``) or an array of tuples (using
-``MultiIndex.from_tuples``).
+``MultiIndex.from_arrays``), an array of tuples (using
+``MultiIndex.from_tuples``), or a crossed set of iterables (using
+``MultiIndex.from_product``).
 
 .. ipython:: python
 
@@ -1552,6 +1553,14 @@ can think of ``MultiIndex`` an array of tuples where each tuple is unique. A
    s = Series(randn(8), index=index)
    s
 
+When you want every pairing of the elements in two iterables, it can be easier
+to use the ``MultiIndex.from_product`` function:
+
+.. ipython:: python
+
+   iterables = [['bar', 'baz', 'foo', 'qux'], ['one', 'two']]
+   MultiIndex.from_product(iterables, names=['first', 'second'])
+
 As a convenience, you can pass a list of arrays directly into Series or
 DataFrame to construct a MultiIndex automatically:
 

doc/source/v0.13.1.txt

@@ -73,6 +73,16 @@ Enhancements
   improves parsing perf in many cases. Thanks to @lexual for suggesting and @danbirken
   for rapidly implementing. (:issue:`5490`, :issue:`6021`)
 
+- ``MultiIndex.from_product`` convenience function for creating a MultiIndex from
+  the cartesian product of a set of iterables (:issue:`6055`):
+
+  .. ipython:: python
+
+      shades = ['light', 'dark']
+      colors = ['red', 'green', 'blue']
+
+      MultiIndex.from_product([shades, colors], names=['shade', 'color'])
+
 - The ``ArrayFormatter`` for ``datetime`` and ``timedelta64`` now intelligently
   limit precision based on the values in the array (:issue:`3401`)
 

pandas/core/index.py

@@ -2491,6 +2491,8 @@ def from_arrays(cls, arrays, sortorder=None, names=None):
         See Also
         --------
         MultiIndex.from_tuples : Convert list of tuples to MultiIndex
+        MultiIndex.from_product : Make a MultiIndex from cartesian product
+                                  of iterables
         """
         from pandas.core.categorical import Categorical
 
@@ -2534,6 +2536,8 @@ def from_tuples(cls, tuples, sortorder=None, names=None):
         See Also
         --------
         MultiIndex.from_arrays : Convert list of arrays to MultiIndex
+        MultiIndex.from_product : Make a MultiIndex from cartesian product
+                                  of iterables
         """
         if len(tuples) == 0:
             # I think this is right? Not quite sure...
@@ -2552,6 +2556,45 @@ def from_tuples(cls, tuples, sortorder=None, names=None):
         return MultiIndex.from_arrays(arrays, sortorder=sortorder,
                                       names=names)
 
+    @classmethod
+    def from_product(cls, iterables, sortorder=None, names=None):
+        """
+        Make a MultiIndex from the cartesian product of multiple iterables
+
+        Parameters
+        ----------
+        iterables : list / sequence of iterables
+            Each iterable has unique labels for each level of the index.
+        sortorder : int or None
+            Level of sortedness (must be lexicographically sorted by that
+            level).
+        names : list / sequence of strings or None
+            Names for the levels in the index.
+
+        Returns
+        -------
+        index : MultiIndex
+
+        Examples
+        --------
+        >>> numbers = [0, 1, 2]
+        >>> colors = [u'green', u'purple']
+        >>> MultiIndex.from_product([numbers, colors],
+                                     names=['number', 'color'])
+        MultiIndex(levels=[[0, 1, 2], [u'green', u'purple']],
+                   labels=[[0, 0, 1, 1, 2, 2], [0, 1, 0, 1, 0, 1]],
+                   names=[u'number', u'color'])
+
+        See Also
+        --------
+        MultiIndex.from_arrays : Convert list of arrays to MultiIndex
+        MultiIndex.from_tuples : Convert list of tuples to MultiIndex
+        """
+        from pandas.tools.util import cartesian_product
+        product = cartesian_product(iterables)
+        return MultiIndex.from_arrays(product, sortorder=sortorder,
+                                      names=names)
+
     @property
     def nlevels(self):
         return len(self.levels)

pandas/tests/test_index.py

@@ -1561,6 +1561,20 @@ def test_from_arrays(self):
         result = MultiIndex.from_arrays(arrays)
         self.assertEquals(list(result), list(self.index))
 
+    def test_from_product(self):
+        first = ['foo', 'bar', 'buz']
+        second = ['a', 'b', 'c']
+        names = ['first', 'second']
+        result = MultiIndex.from_product([first, second], names=names)
+
+        tuples = [('foo', 'a'), ('foo', 'b'), ('foo', 'c'),
+                  ('bar', 'a'), ('bar', 'b'), ('bar', 'c'),
+                  ('buz', 'a'), ('buz', 'b'), ('buz', 'c')]
+        expected = MultiIndex.from_tuples(tuples, names=names)
+
+        assert_array_equal(result, expected)
+        self.assertEquals(result.names, names)
+
     def test_append(self):
         result = self.index[:3].append(self.index[3:])
         self.assert_(result.equals(self.index))