Only applying a "for" command on half of the matrices in it

Question

Filip Hansson 2022-8-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1779840-only-applying-a-for-command-on-half-of-the-matrices-in-it

评论： Image Analyst 2022-8-16

I have a "for" command that makes certain elements in about 60 matrices to a constant. I would like to make it so every time I run the script the "for" only selects a random 30 matrices to make that change and for the ramaining 30 to be left unchanged. How is this possible??

The code at the moment:

for i = 11
m_a(m_spotpris==1) = i;
m_b(m_spotpris==1) = i;
m_c(m_spotpris==1) = i;
m_d(m_spotpris==1) = i;
.
.
.
% And so on

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Answer 1

Image Analyst 2022-8-15

1
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https://ww2.mathworks.cn/matlabcentral/answers/1779840-only-applying-a-for-command-on-half-of-the-matrices-in-it#answer_1026965

You need to make m an array, not 60 separately named variables.

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Filip Hansson 2022-8-16

Thank you! I have done this and is now stuck with the same problem. I have a 24x364x60 array and would like to set 4 of those 24 values to 11, based on another matrix with "1"s in those particular positions, for 30 randomized of those 60 arrays. How is this possible?

Image Analyst 2022-8-16

在 MATLAB Online 中打开

Did you try a simple for loop:

% Thank you! I have done this and is now stuck with the same problem. 
% I have a 24x364x60 array and would like to set 4 of those 24 values to 11, 
% based on another matrix with "1"s in those particular positions, 
% for 30 randomized of those 60 arrays. How is this possible?
% Assign sample data.
array3d = randi(99, 24, 364, 60);
[rows, columns, slices] = size(array3d)
refMatrix = randi([0, 2], 364, 60);
% Get 4 randomly chosen rows.
rowsToChange = sort(randperm(rows, 4))
% Replace array3d where refMatrix is 1.
for k = 1 : length(rowsToChange)
	thisRow = rowsToChange(k);
	for col = 1 : columns
		for slice = 1 : slices
			if refMatrix(col, slice) == 1
				array3d(thisRow, col, slice) = 11;
			end
		end
	end
end

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Answer 2

David Hill 2022-8-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1779840-only-applying-a-for-command-on-half-of-the-matrices-in-it#answer_1026970

在 MATLAB Online 中打开

m=randi(10,10,10,60);%generate your matrix (should store as 3-D matrix)
r=randperm(60,30);%generate the 30 affected matrices
for k=1:length(r)
    M=m(:,:,r(k));%establish temp matrix
    M(M==1)=99;%change all of the 30 affected matrices where elements equal 1 to 99
    m(:,:,r(k))=M;
end