Group Python List Elements

Question

I have a python list as follows:

my_list = 

 [[25, 1, 0.65],
 [25, 3, 0.63],
 [25, 2, 0.62],
 [50, 3, 0.65],
 [50, 2, 0.63], 
 [50, 1, 0.62]]

Answer 1

A way to do this with pandas is to extract each group, pull out 'c', convert to a list and append to the list you want :

z = []
>>> for g in df.groupby('b'):
        z.append(g[1]['c'].tolist())

>>> z
[[0.65, 0.62], [0.62, 0.63], [0.63, 0.65]]

You could do this as a list comprehension:

>>> res = [g[1]['c'].tolist() for g in df.groupby('b')]

>>> res
[[0.65, 0.62], [0.62, 0.63], [0.63, 0.65]]

Another way would be to apply list directly to df.groupby('b')['c'] this gives you the object you need. Then call the .tolist() method to return a list of lists:

>>> df.groupby('b')['c'].apply(list).tolist()
[[0.65000000000000002, 0.62], [0.62, 0.63], [0.63, 0.65000000000000002]]