How to sample uniformly elements on a matrix and store the location information , i.e, (i,j) i-th row and j-th col , in a data type like list in Python?

How to sample uniformly elements on a matrix and store the location information , i.e, (i,j) i-th row and j-th col , in a data type like list in Python? Thanks!

[the cyclist]

Do you want to sample with replacement, or without? (In other words, can you select the same element multiple times?)

Do you have access to the Statistics and Machine Learning Toolbox?

Answer 1

[the cyclist]

This is easiest using linear indexing. (See the section on linear indexing on this page, for example.)

% Input matrix
M = magic(4)

M = 4×4

16 2 3 13 5 11 10 8 9 7 6 12 4 14 15 1

% Number of elements desired
n = 3;

% Generate a random indices into the matrix.
% (This particular method may generate repeats.)
randomIdx = randi(numel(M),3,1);

% Display the index and the randomly selected element
[randomIdx, M(randomIdx)]

ans = 3×2

8 14 14 8 2 5

If you really need the (i,j)-indexing, you can get it:

[i,j] = ind2sub(size(M),randomIdx)

i = 3×1

4 2 2

j = 3×1

2 4 1