Groupby multiple columns in a list

Question

I have a list of list like below

[['H1','L', '1']
['H1','S', '1']
['H2','L', '1']
['H2','L', '1']]

And want grouping based on column1 and column2. Does python provide anything in lists that i can get the below result

H1 L 1
H1 S 1
H2 L 2

Answer 1

You can use itertools.groupby, and the sum up the last column of each group.

from itertools import groupby

out = []
for k, v in groupby(l, key=lambda x: x[:2]):
    s = sum([int(x[-1]) for x in v])
    out.append(k + [s])

print (out)
# [['H1', 'L', 1], ['H1', 'S', 1], ['H2', 'L', 2]]

Answer 2

You can use itertools.groupby along with operator.itemgetter to achieve your desired results

>>> from operator import itemgetter
>>> from itertools import groupby

>>> items = [['H1','L', '1'], ['H1','S', '1'], ['H2','L', '1'], ['H2','L', '1']]
>>> [(*k,sum([int(itemgetter(2)(i)) for i in list(g)])) for k,g in groupby(items,key=itemgetter(0,1))]
>>> [('H1', 'L', 1), ('H1', 'S', 1), ('H2', 'L', 2)]

Answer 3

Another option is to use pandas:

import pandas as pd
df = pd.DataFrame([['H1','L', 1],['H1','S', 1],['H2','L', 1],['H2','L', 1]],columns=['H','LS','1'])
df.groupby(['H','LS']).sum()

returning

       1
H  LS
H1 L   1
   S   1
H2 L   2

or

>>> df.groupby(['H','LS']).sum().reset_index()
    H LS  1
0  H1  L  1
1  H1  S  1
2  H2  L  2