Converting matrix entries satisfying a threshold condition.

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?

[Paul Fishback]

Never mind... Forgot I can apply the floor function to a matrix.

Answer 1

[Star Strider]

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.

[Image Analyst]

Or, instead of the last 3 lines:

M = M > someThreshold;

[Tamir Eisenstein]

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]

@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

[Zakaria Abdelli]

how do i do it with 3 and others 0 can you give me a hint pleas im just a newbee???