MATLAB: Converting matrix entries satisfying a threshold condition.

MATLABmatrix manipulation

I have a matrix of numeric entries and wish to convert each entry above a specified threshold to one and all other entries to zero. This has to be an elegant way to do this without a "for" loop. Perhaps using the "find" command in some manner?

Best Answer

There are likely a number of ways.

One approach:

M = magic(6);
Mm = mean(M(:));
M(M>Mm)  = 1;
M(M~=1) = 0;

It sets all the entries greater than the mean to 1, and then uses that result to set the rest to 0.

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MATLAB: What’s the best way to build a block sparse matrix whose entries are diagonal matrices

Here's a solution that seems to work for me:

clear
N = 3;
M = 5;
BlockContainer = zeros(N * M, 2 * M - 1);
    
for n = 1 : M
    for m = 1: M
        row = m;
        column = M + m - n;
        
        Mblock = rand(N,1) * m * n;
        BlockContainer((row - 1) * N + 1:(row) * N,column) = Mblock;
    end
end
MFull = spdiags(BlockContainer,-(M - 1) * N:N:(M - 1) * N, N * M, N * M)

MATLAB: How to create a m*n matrix with 0,1 entries

Did you say random until we had to prod you? :)

The requirements imply that m<=n.

A = eye(m,n);
A(randperm(m),randperm(n))

That yields a fixed number of ones. If you want the result to sometimes have less than m ones, then just start with a diagonal matrix with some of the diagonal elements as zero. Then you can define the number of non-zeros in advance. You can even choose the number of them randomly.

help diag

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Related Solutions

MATLAB: What’s the best way to build a block sparse matrix whose entries are diagonal matrices

MATLAB: How to create a m*n matrix with 0,1 entries

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