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pythonpandascumulative-sum

Cumulative sum by column in pandas dataframe

I have created the following dataframe:

d = {'x': [0,0,1,1,1,1,1,2,2,2], 'y': [67,-5,78,47,88,12,-4,14,232,28]}
df = pd.DataFrame(data=d)
print(df)

which looks like this:

enter image description here

I want to calculate a column "z" which is the cumulative of column "y" by column "x". So, I calculate the cumulative distribution as long as x is of the same value. The resulting dataframe should look like this:

enter image description here

So, when the column X changes value a new cumulative distribution is calculated.

How can I do that in python?

Solution

  • You can perform the cumsum per group using groupby + cumsum:

    df['z'] = df.groupby('x')['y'].cumsum()

    output:

       x    y    z
0  0   67   67
1  0   -5   62
2  1   78   78
3  1   47  125
4  1   88  213
5  1   12  225
6  1   -4  221
7  2   14   14
8  2  232  246
9  2   28  274