How can I average multiple matrices by element, ignoring NaN values, to create a new matrix of the same size?

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Patrick
Patrick 2013-10-16
评论： Jerry Gregoire 2015-4-14
I have 248 matrices, each of size 72x144. There are some NaN values inserted randomly here and there in these matrices. I would like to create a new matrix, also of size 72x144, which is an average by element of the originals, but ignoring the NaN values. For example:
Original:
matrixA = [2 3 5 | 3 NaN 1 | 2 4 3]
matrixB = [3 4 NaN | 1 2 5 | NaN 3 5]
matrixC = [NaN 2 3 | 2 5 3 | 1 2 1]
Want:
matrixAvg = [2.5 3 4 | 2 3.5 3 | 1.5 3 3]
Is there a simple way for me to do this?
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Yannick
Yannick 2013-10-16
Hi, if you have Statistics Toolbox, you can use nanmean as follows:
matrixA = [2 3 5 ; 3 NaN 1 ; 2 4 3];
matrixB = [3 4 NaN ; 1 2 5 ; NaN 3 5];
matrixC = [NaN 2 3 ; 2 5 3 ; 1 2 1];
allData = cat(3,matrixA,matrixB,matrixC);
nanmean(allData,3);
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Jerry Gregoire
Jerry Gregoire 2015-4-14
You can also use mean with 'omitnan'
S = mean(..., MISSING) specifies how NaN (Not-A-Number) values are
treated. The default is 'includenan':
'includenan' - the mean of a vector containing NaN values is also NaN.
'omitnan' - the mean of a vector containing NaN values is the mean
of all its non-NaN elements. If all elements are NaN,
the result is NaN.

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Azzi Abdelmalek
Azzi Abdelmalek 2013-10-16
编辑：Azzi Abdelmalek 2013-10-16
Edit
matrixA = [2 3 5 ; 3 NaN 1 ; 2 4 3]
matrixB = [3 4 NaN ; 1 2 5 ; NaN 3 5]
matrixC = [NaN 2 3 ; 2 5 3 ; 1 2 1]
A={matrixA matrixB matrixC}
B=cat(3,A{:})
idx=find(isnan(B))
C=ones(size(B));
C(idx)=0;
B(idx)=0;
out=sum(B,3)./sum(C,3)
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Azzi Abdelmalek
Azzi Abdelmalek 2013-10-16
编辑：Azzi Abdelmalek 2013-10-16
The code replace NaN by zeros, but when calculating the mean, it is ignored, for example
[ nan 2 3] % is replaced by
[0 2 3]
% to calculate the mean
sum([0 2 3])./sum([0 1 1]) % =5/2=2.5

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