Get Sum by Group in Python – DataFrame Subgroups (2 Examples)

This tutorial explains how to calculate the sum by group in the Python programming language.

Setting up the Examples

import pandas as pd                               # Import pandas library in Python
my_df = pd.DataFrame({'A':range(19, 28),          # Constructing a pandas DataFrame
                      'B':[6, 7, 3, 9, 1, 3, 8, 8, 9],
                      'C':range(20, 11, - 1),
                      'GRP_a':['gr1', 'gr1', 'gr2', 'gr3', 'gr1', 'gr2', 'gr2', 'gr3', 'gr3'],
                      'GRP_b':['a', 'b', 'c', 'c', 'a', 'b', 'b', 'a', 'a']})
print(my_df)
#     A  B   C GRP_a GRP_b
# 0  19  6  20   gr1     a
# 1  20  7  19   gr1     b
# 2  21  3  18   gr2     c
# 3  22  9  17   gr3     c
# 4  23  1  16   gr1     a
# 5  24  3  15   gr2     b
# 6  25  8  14   gr2     b
# 7  26  8  13   gr3     a
# 8  27  9  12   gr3     a

Example 1: Calculating Sum by Group in Python

print(my_df.groupby('GRP_a').sum())               # Computing the column sum by group
#         A   B   C
# GRP_a            
# gr1    62  14  55
# gr2    70  14  47
# gr3    75  26  42

Example 2: Calculating Sum by Group & Subgroup in Python

print(my_df.groupby(['GRP_a', 'GRP_b']).sum())    # Computing the column sum by multiple groups
#               A   B   C
# GRP_a GRP_b            
# gr1   a      42   7  36
#       b      20   7  19
# gr2   b      49  11  29
#       c      21   3  18
# gr3   a      53  17  25
#       c      22   9  17

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