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Mean of every row in a double matrix without looping

Asked by Ms. Mat

Ms. Mat (view profile)

on 27 Dec 2012
Accepted Answer by Matt J

Matt J (view profile)

Is it possible to find mean and std dev. of every row in a huge matrix with double data and a lot of NaN interspersed without looping through every row ?

A = [1 2 NaN; 4 NaN 6 ; 8 9 10]
output = 1.5
         5
         9

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Ms. Mat

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1 Answer

Answer by Matt J

Matt J (view profile)

on 28 Dec 2012
Edited by Matt J

Matt J (view profile)

on 29 Dec 2012
Accepted answer

If you have the Statistics toolbox, you can use nanmean(A,2) and nanstd(A,2).

If you don't have the toolbox, you can still avoid looping by doing

 B=A;
 map=~isnan(A);
 B(~map)=0;
 N=sum(map,2);
 rowmeans = sum(B,2)./N;
 rowstds = sqrt( sum(B.^2,2)./N -rowmeans.^2 );

If A is of type sparse, however, the above may need to be modified for efficiency's sake.

1 Comment

Ms. Mat

Ms. Mat (view profile)

on 29 Dec 2012

Thank You !!!

Matt J

Matt J (view profile)

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