Adding column values as long as a value in other column matches

Question

How do I add column values as long as a value in the other column is the same?

e.g. from the following list:

Time   Value
10       a
20       b
10       c
10       d
20       f

I want to obtain the following result:

Time      Value
10       (a+c+d)
20        (b+f)

Answer 1

You can use groupby, then select the Value elements (so you don't sum the Times), then finally apply sum.

>>> d = {'Time': [10,20,10,10,20], 'Value': ['a', 'b', 'c', 'd', 'f']}
>>> df = pd.DataFrame(d)
>>> df
   Time Value
0    10     a
1    20     b
2    10     c
3    10     d
4    20     f
>>> df.groupby(['Time'])['Value'].apply(sum).reset_index()
   Time Value
0    10   acd
1    20    bf