Set matrix element to zero for some condition

Question

Philipp 2023-6-1

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https://ww2.mathworks.cn/matlabcentral/answers/1976709-set-matrix-element-to-zero-for-some-condition

评论： Vilém Frynta 2023-6-1

Hello,

I'm new to Matlab and have a simple question. I have a matrix M of numbers and I like to create a new matrix, where all elements are set to zero that do not satisfy a certain condition (say, e.g., all elements larger than 1). How do I do this in the most efficient way?

I tried

filter = find((M<=1));
Mnew = M(filter);

but unfortunately it doesn't work because filter gives me a list of linear indices, but I like to keep the shape of the matrix M. I know that

[row,col] = find((M<=1));

gives me the row and column indices separately, but

Mnew = M([row,col]);

also does not do the job (I kind of understand that it does not work, but I have no idea how to fix it).

Any help is greatly appreciated!

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Answer 1

Vilém Frynta 2023-6-1

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https://ww2.mathworks.cn/matlabcentral/answers/1976709-set-matrix-element-to-zero-for-some-condition#answer_1248324

编辑：Vilém Frynta 2023-6-1

在 MATLAB Online 中打开

Hi,

my approach would be as follows:

% Matrix 5x5 with random numbers 0-10
M = randi(10, 5)
M = 5×5
     9     6     4     8     8
     2     5    10     7     1
     9     7     8     2     7
     6     4     3     9     9
     6     1     5     8     5
% Create logical vector of numbers higher than 5 (condition)
idx = M > 5;
% Apply it to your matrix and set those values to 0
M(idx) = 0
M = 5×5
     0     0     4     0     0
     2     5     0     0     1
     0     0     0     2     0
     0     4     3     0     0
     0     1     5     0     5

Ultimately, you can do it in one line.

M(M>5)=0;

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Philipp 2023-6-1

Oh, thanks lot. I expected there was a simple one-line answer, but I was unable to find it! :)

Vilém Frynta 2023-6-1

Yes, in MATLAB, there's always simpler solution to the problem than you have. Almost always when I help people on this forum, someone better comes and does something I recommended much easier.

Happy I helped.

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