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mean value of subarrays

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Hassan on 22 Apr 2011
I have a 3-dimensinal array ( 1483 rows, 417 columns and 4 bands). I am trying to get a mean value for each sub-array of 92rows*92columns. I have some zero values that I want to exclude when the calcualtion of mean is being done. I used the following code but it's not data type is uint32. i apperciate your help.

Accepted Answer

Sean de Wolski
Sean de Wolski on 22 Apr 2011
A couple of calls to convn. The first call will determine the number of zeros; the second will calculate the sum of all values in the sub array; array divide the second by the first.
If you don't want to do it to EVERY POSSIBLE subarray, use blkproc or blockproc with function handle
Also be aware that since your data type is uint32, if the sum of the 92*92*4 values exceeds 4,294,967,295 it will truncate to 4,294,967,295 and your mean will be wrong.
Sean de Wolski
Sean de Wolski on 22 Apr 2011
doc blkproc. The function I wrote would be the handle you would feed it.
Something like:
mean_wout_zeros = blkproc(Data,[92 92],@(x)sum(x(:))./(sum(logical(x(:))));
But I just remembered that blkproc is only for 2-dimensions so forget the whole thing.

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More Answers (1)

Sean de Wolski
Sean de Wolski on 22 Apr 2011
Here's a 2-dimensional example that demonstrates the logic and kernels.
%sample data
A = uint32(repmat(magic(10),[4,1]));
A(A<10) = 0;
%We will use a window size 6x10
window = ones(6,10);
nnzeros = conv2(double(logical(A)),window,'valid'); %you can change this shape do whatever it is you want at the edges.
winsum = conv2(double(A),window,'valid');
mean_wout_zeros = winsum./nnzeros;
%check that it worked (for first valid value)
You could convert mean_wout_zeros back to uint32 if you want...
Hassan on 22 Apr 2011
As I said I need an array of ean values (16 rows,5coulmns,4 abnds) mean values while using the qhat you said above, I got vecotr of 5540 elements.
it seems blkproc,as you wrote the code above, does what I need.
thanks for the help Sean.

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