A Masked N-D array containing only the first M lowest values

Top-Values-No-Sort

%% A code to find the N highest or lowest values in a N-D array without using sort.

N = [10 10 10];

% nbins is an approximate
% higher values improve accuracy but lower efficiency
nbins = 101;

chopto = 100;  % Chop to the first hundred values approximately

A = rand( N );

[y,x] = hist(A(:), nbins);

%% the index to chop

id = find( cumsum(y) >= chopto, 1, 'first' );

%% logical array into the lower values

b = A < x(id);

disp(sprintf( 'The number of nonzero values is %i.', nnz(b)) );

%% The new masked array is

A(~b) = 0;