MATLAB Answers


Loop through hundreds of matrices to change values larger than 1 to 0

Asked by Zoe
on 19 Oct 2017
Latest activity Commented on by Zoe
on 23 Oct 2017
I have more than 400 matrices, currently I am using "find" to change the values larger than 1 in the matrix to 0 one by one manually with this code:
val = find(yf > 1);
yf(val) = 0;
Is there a way to do it with loop? Please help, thank you.


Could you confirm that you want values between 0 and 1 exactly to be left alone? If the rule were that positive values were to be replaced by 0 then the operation is a bit more efficient.
"... 400 matrices ..."
How are these matrices stored? In individual variables? As part of a cell or struct array? Or ...?
Hi Walter, those matrices are actually image data, the value I WANT is actually between 0 and 1 (definitely smaller than 1), and values larger than 1 are noise (background data, etc.)
Hi James, in a 1*452 cell array , so I use
images{1, #}
to read them one by one right now.

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3 Answers

Answer by Image Analyst
on 19 Oct 2017
 Accepted Answer

If you want a loop and your images are in the cell array, you can do it like this:
for k = 1 : length(images)
% Extract his one image.
thisImage = images{1, k};
% Reduce/Clip values 1.000001 and larger to 1.
thisImage(thisImage > 1) = 1;
% Stick back into cell array
images{1, k} = thisImage;


You're welcome, but you probably never should have stored all your images in a cell array in the first place. It takes up a lot of memory and there was probably never a need to have them all in memory simultaneously. You probably could have read your images one at a time and processed them immediately in the loop without storing them all. Anyway, thanks for Accepting the answer.
Thank you for letting me know this:)

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Answer by Star Strider
on 19 Oct 2017

Instead of find, I would simply use ‘logical indexing’.
yf = 0.5 + rand(4,5)
yf(yf > 1) = 0
yf =
0.64115 1.2321 1.0209 1.3162 1.1876
1.0121 1.2498 0.71908 1.2939 1.4869
1.2213 0.90732 1.3424 0.96911 1.2699
1.4288 0.73949 1.1629 0.80952 1.3296
yf =
0.64115 0 0 0 0
0 0 0.71908 0 0
0 0.90732 0 0.96911 0
0 0.73949 0 0.80952 0
This should be more efficient, although you will still have to loop through every matrix.


Thank you for replying! But my question is how are you gonna do the loop?? Sorry I am relatively new to matlab, and I do know lots of functions but I dont know how to loop through my matrices.
That depends on how your matrices are stored. If each is in a separate file, read the file and then do the replacement.

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Answer by James Tursa
on 19 Oct 2017

result = cellfun(@(c)c.*(c<=1),images,'uni',false);


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