Sum the values in a pandas column based on the items in another column

Question

how can I sum the values in column \'two\' based on the items in column \'one\' in pandas dataframe:

df = pd.DataFrame({\'One\': [\'A\', \'B\', \'A\', \'B\'], \'         


        

Answer 1

The trick is use pandas built-in functions .groupby(COLUMN_NAME) and then .sum() that new pandas object

import pandas as pd
df = pd.DataFrame({'One': ['A', 'B', 'A', 'B'], 'Two': [1, 5, 3, 4]})

groups = df.groupby('One').sum()
print(groups.head())

Answer 2

You need to group by the first column and sum on the second.

df.groupby('One', as_index=False).sum()

  One  Two
0   A    4
1   B    9