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# Getting cumulative sum of each group in Pandas DataFrame

schedule Aug 12, 2023
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local_offer
PythonPandas
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Consider the following DataFrame:

``` import pandas as pddf = pd.DataFrame({'name':['alex','alex','bob','bob','cathy'], 'score':[3,4,5,6,9]})df name score0 alex 31 alex 42 bob 53 bob 64 cathy 9 ```

To group by name, and then compute the cumulative sum for each group:

``` s = df.groupby('name')['score'].cumsum() # returns a Seriess 0 31 72 53 114 9Name: score, dtype: int64 ```

To add this Series as a new column to the original DataFrame:

``` df['cum_score'] = sdf name score cum_score0 alex 3 31 alex 4 72 bob 5 53 bob 6 114 cathy 9 9 ```
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