pandas rolling computation with window based on values instead of counts

Question

I\'m looking for a way to do something like the various rolling_* functions of pandas, but I want the window of the rolling computation to be defin

Answer 1

I think this does what you want:

In [1]: df
Out[1]:
   RollBasis  ToRoll
0          1       1
1          1       4
2          1      -5
3          2       2
4          3      -4
5          5      -2
6          8       0
7         10     -13
8         12      -2
9         13      -5

In [2]: def f(x):
   ...:     ser = df.ToRoll[(df.RollBasis >= x) & (df.RollBasis < x+5)]
   ...:     return ser.sum()

The above function takes a value, in this case RollBasis, and then indexes the data frame column ToRoll based on that value. The returned series consists of ToRoll values that meet the RollBasis + 5 criterion. Finally, that series is summed and returned.

In [3]: df['Rolled'] = df.RollBasis.apply(f)

In [4]: df
Out[4]:
   RollBasis  ToRoll  Rolled
0          1       1      -4
1          1       4      -4
2          1      -5      -4
3          2       2      -4
4          3      -4      -6
5          5      -2      -2
6          8       0     -15
7         10     -13     -20
8         12      -2      -7
9         13      -5      -5

Code for the toy example DataFrame in case someone else wants to try:

In [1]: from pandas import *

In [2]: import io

In [3]: text = """\
   ...:    RollBasis  ToRoll
   ...: 0          1       1
   ...: 1          1       4
   ...: 2          1      -5
   ...: 3          2       2
   ...: 4          3      -4
   ...: 5          5      -2
   ...: 6          8       0
   ...: 7         10     -13
   ...: 8         12      -2
   ...: 9         13      -5
   ...: """

In [4]: df = read_csv(io.BytesIO(text), header=0, index_col=0, sep='\s+')