Compress down a 1000x1000 matrix into a 100x100 matrix

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I have a 1000x1000 matrix that contains various values. I would like to compress it down into a 100 by 100 matrix by averaging each 10 by 10 cell's values into 1, but im not really sure how to go about doing this

Accepted Answer

Ameer Hamza
Ameer Hamza on 7 Jun 2020
Edited: Ameer Hamza on 7 Jun 2020
If you have image processing toolbox
M = rand(1000, 1000);
M_new = blockproc(M, [10 10], @(x) mean(x.data, 'all'))
Alternative Solution 1: (surprisingly the fastest)
M_new = conv2(M, ones(10)/100, 'valid');
M_new = M_new(1:10:end, 1:10:end);
Alternative Solution 2:
M_C = mat2cell(M, 10*ones(1,100), 10*ones(1,100));
M_new = cellfun(@(x) mean(x, 'all'), M_C);
Alternative Solution 3:
M_new = zeros(size(M)/10);
for i=1:100
for j=1:100
M_new(i, j) = mean(M(10*(i-1)+1:10*i,10*(j-1)+1:10*j), 'all');
end
end
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More Answers (2)

David Hill
David Hill on 7 Jun 2020
count=1;
for col=1:100:1000
for row=1:100:1000
newMatrix(count)=mean(yourMatrix(row:row+99,col:col+99),'all');
count=count+1;
end
end
newMatrix=reshape(newMatrix,10,[]);

Jan
Jan on 24 Mar 2021
Edited: Jan on 24 Mar 2021
X = rand(1000, 1000);
Y = reshape(X, [10, 100, 10, 100]);
Z = reshape(sum(sum(Y, 1), 3), [100, 100]) / 100;
Or with FEX: BlockMean :
Z = BlockMean(X, 10, 10)

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