Efficiently get indices of histogram bins in Python

Question

Short Question

I have a large 10000x10000 elements image, which I bin into a few hundred different sectors/bins. I then need to perform some iterative calculation

Answer 1

Pandas has a very fast grouping code (I think it's written in C), so if you don't mind loading the library you could do that :

import pandas as pd

pdata=pd.DataFrame({'vals':vals,'ind':ind})
resultsp = pdata.groupby('ind').sum().values

or more generally :

pdata=pd.DataFrame({'vals':vals,'ind':ind})
resultsp = pdata.groupby('ind').agg(func).values

Although the latter is slower for standard aggregation functions (like sum, mean, etc)