select dropping a grouping variable - what happens?

dplython::

(dp.DplyFrame(mtcars) >> dp.group_by(X.cyl, X.am) >> dp.select(X.hp)).columns -> [‘cyl’, ‘am’, ‘hp’], grouping retained # there is no drop?

dfply::

(mtcars >> dp.group_by(‘cyl’,’am’) >> dp.select(‘hp’)).columns -> [‘hp’], grouping is lost select (mtcars >> dp.group_by(‘cyl’,’am’) >> dp.select(‘cyl’,’am’, ‘hp’)).columns -> [‘cyl’, ‘am’, ‘hp’], grouping is retained!

(mtcars >> dp.group_by(‘cyl’,’am’) >> dp.drop(‘cyl’)).columns -> all but [‘cyl’], grouping is lost on drop

(mtcars >> dp.group_by(‘cyl’,’am’) >> dp.drop(‘hp’)).columns -> all but [‘cyl’], grouping is retained!

It is dependend on the actual columns being kept/dropped whether grouping is retained.

dppd::

dp(mtcars).groupby([‘cyl’,’am’]).select(‘hp’).pd.columns -> [cyl, am, hp], groups still intact

dp(mtcars).groupby([‘cyl’,’am’]).drop(‘am’).pd.columns -> all columns, groups still intact

dp(mtcars).groupby([‘cyl’,’am’]).loc[:,’am’].pd.columns -> [am], grouping dropped

Verbs/pandas methods implicitly add grouping columns, accesors drop them.