计算过程中的熊猫动态索引参考

Question

I have the following data frame

    val  sum
0    1    0
1    2    0
2    3    0
3    4    0
4    5    0
5    6    0
6    7    0

I would like to calculate the sum of the next three rows' (including the current row) values. I need to do this for very big files. What is the most efficient way? The expected result is

    val  sum
0    1    6
1    2    9
2    3    12
3    4    15
4    5    18
5    6    13
6    7    7

In general, how can I dynamically referencing to other rows (via boolean operations) while making assignments?

Answer 1

> pd.rolling_sum(df['val'], window=3).shift(-2)
0     6
1     9
2    12
3    15
4    18
5   NaN
6   NaN

If you want the last values to be "filled in" then you'll need to tack on NaN's to the end of your dataframe.