如何获得 pandas dataframe 中的 k 个连续行的总和？

Question

I have this pandas dataframe:

ts = pd.Series([1, 2, 3, 4, 5, 6, 7, 8])

What I would like to get is a dataframe which contains another column with the sum of four consecutive rows of ts . The sum should be put in every row of the consecutive rows.

In this case, this means a new dataframe should look like this one:

index ts sum
0 1 10
1 2 10
2 3 10
3 4 10
4 5 26
5 6 26
6 7 26
7 8 26

How could I do this?

Answer 1

Use GroupBy.transform with integers division by k :

k = 4
a = ts.groupby(ts.index // k).transform('sum')
#alternative if not RangeIndex
#a = ts.groupby(np.arange(len(ts)) // k).transform('sum')
print (a)
0    10
1    10
2    10
3    10
4    26
5    26
6    26
7    26
dtype: int64
    

If need DataFrame with 2 columns add Series.to_frame :

df = ts.to_frame('ts')
df['sum'] = df.groupby(ts.index // k).transform('sum')
print (df)
   ts  sum
0   1   10
1   2   10
2   3   10
3   4   10
4   5   26
5   6   26
6   7   26
7   8   26
    

Answer 2

You could also try this list comprehension:

ts = pd.Series([1, 2, 3, 4, 5, 6, 7, 8])
sum_ = sum([[sum(ts[i:i + 4])] * 4 for i in range(0, len(ts), 4)], [])
df = pd.DataFrame({'ts': ts, 'sum': sum_})
print(df)

Output:

   sum  ts
0   10   1
1   10   2
2   10   3
3   10   4
4   26   5
5   26   6
6   26   7
7   26   8