Fixing melt() when col_level>0 in a multi-index column

Author: rbavishi

pandas/core/reshape/melt.py

@@ -24,6 +24,10 @@
  other='DataFrame.melt'))
 def melt(frame, id_vars=None, value_vars=None, var_name=None,
  value_name='value', col_level=None):
+ if col_level is not None: # allow list or other?
+ frame = frame.copy()
+ frame.columns = frame.columns.get_level_values(col_level)
+
  # TODO: what about the existing index?
  if id_vars is not None:
  if not is_list_like(id_vars):
@@ -47,13 +51,9 @@ def melt(frame, id_vars=None, value_vars=None, var_name=None,
  else:
  value_vars = list(value_vars)
  frame = frame.loc[:, id_vars + value_vars]
- else:
+ elif col_level is None: # avoid making copy if possible
  frame = frame.copy()
 
- if col_level is not None: # allow list or other?
- # frame is a copy
- frame.columns = frame.columns.get_level_values(col_level)
-
  if var_name is None:
  if isinstance(frame.columns, ABCMultiIndex):
  if len(frame.columns.names) == len(set(frame.columns.names)):