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Converting matrix entries satisfying a threshold condition.

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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?

  1 Comment

Paul Fishback
Paul Fishback on 29 Jan 2015
Never mind... Forgot I can apply the floor function to a matrix.

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Accepted Answer

Star Strider
Star Strider on 29 Jan 2015
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.

  3 Comments

Tamir Eisenstein
Tamir Eisenstein on 6 Mar 2020
What if my threshold is not a specific number but a percentile? for example, set the top 20% values to 1 and the rest to 0.
Star Strider
Star Strider on 7 Mar 2020
@Tamir Eisenstein —
M = randi(99, 10); % Create Matrix
Msort = sort(M(:),'descend'); % Sorted Vector
Threshold = Msort(fix(numel(M)*0.2)); % Find Top 20% Value
Out = zeros(size(M))~=0; % Create Logical Matrix
Out(M >= Threshold) = 1; % Desired Result

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