CODEWITHSUNDEEP
pythonpandascumsum
Raphadasilva
Raphadasilva

Reputation: 617

Pandas : reverse cumulative sum's process

I've got a simple pandas' Serie, like this one :

    st
0   74
1   91
2   105
3   121
4   136
5   157

Datas for this Serie are the result of a cumulative sum, so I was wondering if a pandas function could "undo" the process, and return a new Serie like :

    st     result
0   74     74
1   91     17
2   105    14
3   121    16
4   136    15
5   157    21

result[0] = st[0], but after result[i] = st[i]-st[i-1].

It's seemed to be very simple (and maybe I missed a post), but I didn't find anything...

Upvotes: 1

Views: 355

Answers (1)

jezrael
jezrael

Reputation: 863741

Use Series.diff with replace first missing value by original by Series.fillna and then if necessary cast to integers:

df['res'] = df['st'].diff().fillna(df['st']).astype(int)
print (df)
    st  res
0   74   74
1   91   17
2  105   14
3  121   16
4  136   15
5  157   21

Upvotes: 2

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