Max/Min of nonzero rows/cols

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]

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 )

Answer 1

[Richard Brown]

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]

Thank you. I didn't think to change the zeros to NaN so that they didn't mess up the min operation.

Answer 2

[Geoff]

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));

[edit]

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 =)

[Richard Brown]

Ha, mine too! Whereabouts?

[Geoff]

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]

I am indeed, wobbles and all :)