Array Indexing using logicals in higher dimensions
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I have a 3D array: A = 10x10x100 where the 2D data (10x10) is stacked in the 3rd dimension.
I am using a logical mask: B which is 10x10 and has 1s at the locations where I want to access the data in every 2D slice of the 3D array.
I would like to use the logical mask to access the data from each 2D slice and perform some simple operations - such as compute mean - for all slices (in the 3rd dimension). I am currently using a for loop as below.
for i = 1:size(A,3)
temp = A(:,:,i);
mean_out(i) = mean(temp(B));
end
Is it possible to achieve this without a for loop?
Thanks.
采纳的回答
Ameer Hamza
2020-5-20
编辑：Ameer Hamza
2020-5-20
Try this
mean_val = squeeze(mean(A.*B, [1 2]))
Similarly
squeeze(max(A.*B, [], [1 2])) % maximum value
squeeze(min(A.*B, [], [1 2])) % minimum value
4 个评论
AP
2020-5-20
Ameer Hamza
2020-5-20
Try this. It replaces 0s with nan and then uses nanmean()
A = rand(10,10,100);
B = rand(10,10)>0.5;
M = A.*B;
M(M==0) = nan;
mean_val = squeeze(nanmean(M, [1 2]))
Also, it does not reduce the matrix to the column. It calculates the mean of each 3D slice separately. I used squeeze() to convert the final answer to a column matrix. You can run it without squeeze, and you will get a 3D matrix
mean_val = nanmean(M, [1 2])
Ameer Hamza
2020-5-20
In that case try
A = rand(10,10,100);
B = rand(10,10)>0.5;
mask = repmat(B, 1, 1, size(A,3));
M = A;
M(mask) = nan;
mean_val = nanmean(M, [1 2])
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