zljubi...@gmail.com wrote:
> I have a dataframe:
>
>
> df = pd.DataFrame({
> 'x': [3,4,5,8,10,11,12,13,15,16,18,21,24,25],
> 'a': [10,9,16,4,21,5,3,17,11,5,21,19,3,9]
> })
>
> df
> Out[30]:
> a x
> 0 10 3
> 1 9 4
> 2 16 5
> 3 4 8
> 4 21 10
> 5 5 11
> 6 3 12
> 7 17 13
> 8 11 15
> 9 5 16
> 10 21 18
> 11 19 21
> 12 3 24
>
>
> for every "x" value I should subtract a certain number (say 3), and then
> find a maximum "a" value where x is in a range from x-3 to x.
>
> For example:
> index, x, x-3, max(a) where x is between x-3 and x
> 0, 3, 0, 10
> 1, 4, 1, 10
> 2, 5, 2, 16
> 3, 8, 5, 16
> 4, 10, 7, 21
> ...
>
> "x" is incremental, "a" is random
> How to find max "a" values?
I have no idea how you'd do that in pandas.
Here's generic Python:
>>> m = df.as_matrix()
>>> pd.DataFrame(
... [[x, x-3, max(aa for aa, xx in m if x-3<=xx<=x)] for a, x in m],
... columns=["x", "x-3", "max(a)..."]
... )
x x-3 max(a)...
0 3 0 10
1 4 1 10
2 5 2 16
3 8 5 16
4 10 7 21
5 11 8 21
6 12 9 21
7 13 10 21
8 15 12 17
9 16 13 17
10 18 15 21
11 21 18 21
12 24 21 19
13 25 22 9
[14 rows x 3 columns]
>>>
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