To find the average when there is NaN

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Thishan Dharshana Karandana Gamalathge
评论： Walter Roberson 2017-8-18
I want to find the average of each pairs. ie. avg of 2 &4, avg of NaN and 5. Answer should be 3 and 5. For the second pair, code should eliminate NaN, so avg should be 5. That's where I have the problem. Following is the code I wrote. Thanks.
A=[2 4 NaN 5];
j=1;
for i=1:2:4
B=A(i:i+1);
C=~isnan(B);
test(j)=mean(A(C));
i=i+1;
j=j+1;
end

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回答（2 个）

Chad Greene
Chad Greene 2017-8-17
编辑：Chad Greene 2017-8-17
Hi Thishan,
On newer versions of Matlab, use
test(j)=mean(A(C),'omitnan');
If you have an older version of Matlab and you have the Statistics Toolbox, use
test(j)=nanmean(A(C));
Alternatively, if neither of those options work for you,
tmp = A(C);
test(j)= = mean(tmp(isfinite(tmp)));
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Image Analyst
Image Analyst 2017-8-17
Sure it makes sense. You can move along the vector an element at a time taking the means of pairs, no matter whether there are an odd or even number of elements. Just look:
m = [1,2,3,4,5]
pairMeans = conv(m, [.5,.5], 'valid')
m =
1 2 3 4 5
pairMeans =
1.5 2.5 3.5 4.5
(Note the above does not handle nans in the desired way).
Walter Roberson
Walter Roberson 2017-8-18
However, the user's for loop increments by 2, so that is not the pairs they meant. They also indicated they expected exactly 2 results, not 3.

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Image Analyst
Image Analyst 2017-8-17
编辑：Image Analyst 2017-8-17
This will work for any length of A, even odd numbers:
A=[2 4 NaN 5 6 8 9]; % 7 elements.
kernel = [1,1];
sumA = conv(A, kernel, 'same')
nonNaNA = ~isnan(A)
denom = conv(nonNaNA, kernel, 'same')
output = sumA ./ denom
output(isnan(output)) = [] % Remove nans.

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