python - How can I reorder multi-indexed dataframe columns at a specific level

Question

I have a multi-indexed DataFrame with names attached to the column levels. I'd like to be able to easily shuffle the columns around so that they match the order specified by the user. Since this is down the pipeline, I'm not able to use this recommended solution and order them properly at creation time.

I have a data table that looks (something) like

Experiment           BASE           IWWGCW         IWWGDW
Lead Time                24     48      24     48      24     48
2010-11-27 12:00:00   0.997  0.991   0.998  0.990   0.998  0.990
2010-11-28 12:00:00   0.998  0.987   0.997  0.990   0.997  0.990
2010-11-29 12:00:00   0.997  0.992   0.997  0.992   0.997  0.992
2010-11-30 12:00:00   0.997  0.987   0.997  0.987   0.997  0.987
2010-12-01 12:00:00   0.996  0.986   0.996  0.986   0.996  0.986

I want to take in a list like ['IWWGCW', 'IWWGDW', 'BASE'] and reorder this to be:

Experiment           IWWGCW         IWWGDW         BASE           
Lead Time                24     48      24     48      24     48  
2010-11-27 12:00:00   0.998  0.990   0.998  0.990   0.997  0.991  
2010-11-28 12:00:00   0.997  0.990   0.997  0.990   0.998  0.987  
2010-11-29 12:00:00   0.997  0.992   0.997  0.992   0.997  0.992  
2010-11-30 12:00:00   0.997  0.987   0.997  0.987   0.997  0.987  
2010-12-01 12:00:00   0.996  0.986   0.996  0.986   0.996  0.986  

with the caveat that I don't always know at what level "Experiment" will be. I tried (where df is the multi-indexed frame shown above)

df2 = df.reindex_axis(['IWWGCW', 'IWWGDW', 'BASE'], axis=1, level='Experiment')

but that didn't seem to work - it completed successfully, but the DataFrame that was returned had its column order unchanged.

My workaround is to have a function like:

def reorder_columns(frame, column_name, new_order):
    """Shuffle the specified columns of the frame to match new_order."""

    index_level  = frame.columns.names.index(column_name)
    new_position = lambda t: new_order.index(t[index_level])
    new_index    = sorted(frame.columns, key=new_position)
    new_frame    = frame.reindex_axis(new_index, axis=1)
    return new_frame

where reorder_columns(df, 'Experiment', ['IWWGCW', 'IWWGDW', 'BASE']) does what I expect but it feels like I'm doing extra work. Is there an easier way to do this?

Answer 1

There is a very simple way: just create a new dataframe based on the original, with the correct order of multiindex columns:

multi_tuples = [('IWWGCW',24), ('IWWGCW',48), ('IWWGDW',24), ('IWWGDW',48)
    , ('BASE',24), ('BASE',48)]

multi_cols = pd.MultiIndex.from_tuples(multi_tuples, names=['Experiment', 'Lead Time'])

df_ordered_multi_cols = pd.DataFrame(df_ori, columns=multi_cols)