Ignoring NaN values when multiplying?

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Anna
Anna 2011-4-22
回答： Steven Lord 2017-6-6
I need to multiply a range of elements with eachother, and now i discovered that if any of the elements is entered as NaN, the entire product will be NaN.
winnerportfolios=zeros(11,127);
for column=1:127
y=2;
x=firstWinnerRow(1,column);
for col=2:3:375
for nrStocks=10:10:100
winnerportfolios(y,column)=prod(HPRsorted(x:x+nrStocks,col));
y=y+1;
end
end
end
I'd like to find a way to ignore the NaN values. The only way i come to think of would be to change the NaN-values to 1...
Thank you so much in advance!
oh and ignore the awful code, I've been working with matlab for only about a month :)

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回答（2 个）

Teja Muppirala
Teja Muppirala 2011-4-22
"The only way i come to think of would be to change the NaN-values to 1"
That sounds like a reasonable idea to me:
X = [2 3 4; nan 2 7; 2 5 nan]
Y = X;
Y(isnan(Y)) = 1;
prod(Y)
  2 个评论
Anna
Anna 2011-4-22
Thank you for your help, I'd better do it like that then :)
Jerry Gregoire
Jerry Gregoire 2015-4-14
Jonas had a good entry dealing with this issue and why you may want to consider the implications of doing this.
http://stackoverflow.com/questions/14178843/matlab-matrix-multiplication-ignoring-nans

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Steven Lord
Steven Lord 2017-6-6
If you're using release R2017a or later, use the 'omitnan' flag in your call to prod.

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