How to get a matrix values' indices?

[Mikolaj Karolczak]

Hello,

Suppose we have a matrix of integer values. Is there any function to get quickly
matrices of each value's indices?

e.g.

I have:
[1 2 3
 1 2 2
 1 1 3]

I want:
-> 1: [1 1; 2 1; 3 1; 3 2]
-> 2: [1 2; 2 2; 2 3]
-> 3: [1 3; 3 3]

Surely I can get it by checking the value for every index but for big matrices
if works slowly.

Actually I need to calculate the 'specific gravity' of each value in the matrix
- the mean values of each value's indices. Maybe there is a function to do it
yet simplier?

Rgds,
Mikolaj





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