# Max/Min of nonzero rows/cols

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Edward Umpfenbach on 12 Apr 2012
Commented: Dan on 28 Dec 2015
I have a Matrix, A.
I want to find the max and min for every row and column in A, excluding the zero entries.
I have coded it using For loops, but it is too slow. I need it to be all vectorized. Any help is greatly appreciated.
Dan on 28 Dec 2015
A = matrix with some zero entries . Indzero = find( A== 0); B=A; B(Indzero) = max(max(A))+1; Min(B,[],1) B(Indzero) = min(min(A))-1; Max(B,[],1)
U can use this sort of logic maybe . u can also go at it by gpu processing or mexing for faster results ( this is exactly the type of probelms where u get the best rests with gpus Nd mexing )

Richard Brown on 12 Apr 2012
B = A;
B(B == 0) = NaN;
colMax = max(B);
colMin = min(B);
rowMax = max(B, [], 2);
rowMin = min(B, [], 2);
edit: missed the bit about the zero entries
Edward Umpfenbach on 12 Apr 2012
Thank you. I didn't think to change the zeros to NaN so that they didn't mess up the min operation.

Geoff on 12 Apr 2012
When you say 'for every row and column', do you mean a single max and min for the entire matrix? This would do it:
nzmin = min(A(A ~= 0));
nzmax = max(A(A ~= 0));

Note that if you have float data, you might want to consider values 'near' zero:
ztol = eps(max(A(:)));
nz = A < -ztol | A > ztol; % select non-zeros
nzmin = min(A(nz));
nzmax = max(A(nz));
It's refreshing to use a proliferation of 'nz', since it's my nationality =)
##### 3 CommentsShow 1 older commentHide 1 older comment
Geoff on 12 Apr 2012
My heart's in Dunedin. But I moved up to Auckland to get away from Animation Research Ltd ;-) You're a Canterbury lad, right?
Richard Brown on 12 Apr 2012
I am indeed, wobbles and all :)