How to balance unique values in an array Matlab - arrays

Question

I have a vector
Y = [1 1 0 0 0 1 1 0 1 0 1 1 1 0 0 0 1 1 0 0 0 0 1 0 1 0 1 0 1 1 1 0 0 0 1 0 0 0]
1 occurs 17 times
0 occurs 21 times
How can I randomly remove 0s so that both values have equal amounts, such as 1 (17 times) and 0 (17 times)?
This should also work on much bigger matrix.

Answer 1

Starting with your example
Y = [1 1 0 0 0 1 1 0 1 0 1 1 1 0 0 0 1 1 0 0 0 0 1 0 1 0 1 0 1 1 1 0 0 0 1 0 0 0]
You can do the following:
% Get the indices of the value which is more common (`0` here)
zeroIdx = find(~Y); % equivalent to find(Y==0)
% Get random indices to remove
remIdx = randperm(nnz(~Y), nnz(~Y) - nnz(Y));
% Remove elements
Y(zeroIdx(remIdx)) = [];
You could combine the last two lines, but I think it would be less clear.
The randperm line is choosing the correct number of elements to remove from random indices between 1 and the number of zeros.

Answer 2

If the data can only have two values
Values are assumed to be 0 and 1. The most common value is randomly removed to equalize their counts:
Y = [1 1 0 0 0 1 1 0 1 0 1 1 1 0 0 0 1 1 0 0 0 0 1 0 1 0 1 0 1 1 1 0 0 0 1 0 0 0]; % data
ind0 = find(Y==0); % indices of zeros
ind1 = find(Y==1); % indices of ones
t(1,1:numel(ind0)) = ind0(randperm(numel(ind0))); % random permutation of indices of zeros
t(2,1:numel(ind1)) = ind1(randperm(numel(ind1))); % same for ones. Pads shorter row with 0
t = t(:, all(t,1)); % keep only columns that don't have padding
result = Y(sort(t(:))); % linearize, sort and use those indices into the data
Generalization for more than two values
Values are arbitrary. All values except the least common one are randomly removed to equalize their counts:
Y = [0 1 2 0 2 1 1 2 0 2 1 2 2 0 0]; % data
vals = [0 1 2]; % or use vals = unique(Y), but absent values will not be detected
t = [];
for k = 1:numel(vals) % loop over values
ind_k = find(Y==vals(k));
t(k, 1:numel(ind_k)) = ind_k(randperm(numel(ind_k)));
end
t = t(:, all(t,1));
result = Y(sort(t(:)));