Find max(and min) on the moving interval using python

Question

I have a array like

[5.5, 6.0, 6.0, 6.5, 6.0, 5.5, 5.5, 5.0, 4.5]. 

all numbers of this array differ by 0.5, and the maximum difference of two successive numbers is also 0.5(they can be same; as in the example). and there is a moving interval, or box, which covers, for example, 3 successive numbers, like this:

[(5.5, 6.0, 6.0), 6.5, 6.0, 5.5, 5.5, 5.0, 4.5]  # min: 5.5, max: 6.0

and the box moves toward right one by one:

[5.5, (6.0, 6.0, 6.5), 6.0, 5.5, 5.5, 5.0, 4.5]  # min: 6.0, max: 6.5

[5.5, 6.0, (6.0, 6.5, 6.0), 5.5, 5.5, 5.0, 4.5]  # min: 6.0, max: 6.5

the question is, how can I find the min and max of the numbers inside the box for each time box moves?

I can handle it when the size of box and array is small like this example, but I need to apply this to like array size 100000 and box size 10000. using my method(I calculate every max and min using for-loop for each time box passes), it took too much time(I have like 100 more array to do and need to run repeatedly). There is some time limit, so I need to run it like one calculation in 0.5 sec.

Answer 1

Have a look at the rolling windows from pandas:

>>> import pandas as pd
>>> L = [5.5, 6.0, 6.0, 6.5, 6.0, 5.5, 5.5, 5.0, 4.5]
>>> a = pd.DataFrame(L)
>>> pd.rolling_max(a, 3)
     0
0  NaN
1  NaN
2  6.0
3  6.5
4  6.5
5  6.5
6  6.0
7  5.5
8  5.5
>>> pd.rolling_min(a, 3)
     0
0  NaN
1  NaN
2  5.5
3  6.0
4  6.0
5  5.5
6  5.5
7  5.0
8  4.5