ENH: MultiIndex.from_frame

pandas/core/indexes/multi.py

@@ -1189,11 +1189,11 @@ def to_frame(self, index=True, name=None):
         else:
             idx_names = self.names
 
-        result = DataFrame({(name or level):
-                            self._get_level_values(level)
-                            for name, level in
-                            zip(idx_names, range(len(self.levels)))},
-                           copy=False)
+        result = DataFrame(
+            list(self),
+            columns=[n or i for i, n in enumerate(idx_names)]
+        )
+
         if index:
             result.index = self
         return result
@@ -1412,6 +1412,22 @@ def from_product(cls, iterables, sortorder=None, names=None):
         labels = cartesian_product(labels)
         return MultiIndex(levels, labels, sortorder=sortorder, names=names)
 
+    @classmethod
+    def from_frame(cls, df, squeeze=True):
+        """
+        :param df
+        :param squeeze
+            Squeeze single level multiindex to be a regular index
+        """
+        # just let column level names be the tuple of the meta df columns
+        # since they're not required to be strings
+        columns = list(df)
+        mi = cls.from_tuples(list(df.values), names=columns)
+        if squeeze:
+            return mi.squeeze()
+        else:
+            return mi
+
     def _sort_levels_monotonic(self):
         """
         .. versionadded:: 0.20.0
@@ -1474,6 +1490,16 @@ def _sort_levels_monotonic(self):
                           names=self.names, sortorder=self.sortorder,
                           verify_integrity=False)
 
+    def squeeze(self):
+        """
+        If multiindex is only composed of a single level, convert to an index.
+        Otherwise return a copy of the index.
+        """
+        if len(self.levels) == 1:
+            return self.levels[0][self.labels[0]]
+        else:
+            return self.copy()
+
     def remove_unused_levels(self):
         """
         Create a new MultiIndex from the current that removes