Getting values from 4d matrix according (using) 2d matrix with logical values (0 or 1) - does not work as wanted
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Hello!
Let say I have a matrix A of dimensions (50*100*248*20) with data and I have another one B (50*100) with logical values (lets image I have 100 of "1") and I want to get values from my 4D matrix according to B. So I am doing
C = A(B);
But then I am getting my values only from A (:,:,1,1) - first page, but I am expecting to get values from all the pages (along all the 3rd and 4 th dimensions). How can I do this?
So I need at the output a matrix with dimensions (100, 1, 248, 20) - which give me 100 values from each page of 248*20
If I am not clear, let me know!, Hoping for you help! Thanks!
6 Comments
madhan ravi
on 4 Apr 2019
Edited: madhan ravi
on 4 Apr 2019
Indeed sir Walter, thank you for the explanation just noticed the comment.
Linus Olofsson
on 24 Jun 2020
Edited: Linus Olofsson
on 24 Jun 2020
Could someone please give an example of the explanation Walter gave above? I do not really understand how this is a solution of the problem, nor do I understand the code snippet provided by the earlier comment by Walter.
Could the solution please be explained with my very similar non-functional problem with a 3 channel color image and a 2 dimensional logical array (mask) that I would like to use to color code speficic parts of my image, i.e.:
image = zeros(150,5370,3);
whos mask
Name Size Bytes Class Attributes
mask 150x5370 805500 logical
image(mask,2) = 255; % Change the masked part of the image to be green.
Accepted Answer
Yurii Iotov
on 29 Mar 2019
3 Comments
Walter Roberson
on 29 Mar 2019
I think you mean that Zeros are only to be removed at the edges.
The code I posted here finds the bounding box that contains all of the 1's. It could easily be extended to more dimensions.
More Answers (1)
Darren Wethington
on 29 Mar 2019
See if this is what you're looking for:
A = rand(10,20,30,40);
B = round(rand(10,20));
four_dim_logical = zeros(size(A));
for i=1:length(four_dim_logical(1,1,:,1))
for j=1:length(four_dim_logical(1,1,1,:))
four_dim_logical(:,:,i,j) = B;
end
end
C = A(logical(four_dim_logical));
dim1 = sum(B(:));
dim2 = 1;
dim3 = size(A,3);
dim4 = size(A,4);
C = reshape(C,dim1,dim2,dim3,dim4);
2 Comments
Darren Wethington
on 29 Mar 2019
Just saw solutions in the comments. This solution will be MUCH more computationally expensive if either of those work.
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