Python rolling mean starting on the next row

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I have results from a horse race and want to have the rolling win count for the start of each race. This is what I currently have:

Horse Position
A 4
A 1
A 3

This is what I'm after

Horse Position Wins
A 4 0
A 1 0
A 3 1

So when horse A started the second race it had 0 wins but when it started the third race is had 1 win

rolling-computation pandas python
1 Answers

Use the shift operator and cumsum

df["Wins"] = (df["Position"].shift(1) == 1).cumsum()

output:

  Horse  Position  Wins
0     A         4     0
1     A         1     0
2     A         3     1
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