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Sorting NaN

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Andy
Andy on 12 Apr 2012
Commented: Steven Lord on 18 Sep 2018
say if i have a matrix a:
a=[1 2 3;4 5 6;7 8 9;NaN NaN NaN]
i want to sort this in descending order, so i use
sort(a,1,'descend')
but the problem is, matlab puts the NaN at the top, is there a way to make it so that NaN is at the bottom? Thanks

Accepted Answer

Matt Tearle
Matt Tearle on 12 Apr 2012
As long as you don't have any -Inf values in a, you could always do a quick hack:
a=[1 2 3;4 5 6;7 8 9;NaN NaN NaN]
a(isnan(a)) = -Inf;
a = sort(a,1,'descend');
a(isinf(a)) = NaN

More Answers (3)

Huw S
Huw S on 18 Sep 2018
Very late to this for the original poster, but for anyone later looking how to do this....
It's in the matlab functionality.
sort(a,'descend','MissingPlacement','last')
  1 Comment
Steven Lord
Steven Lord on 18 Sep 2018
That functionality was introduced in release R2017a. While I agree that's a good way to solve the problem now, it was not an option when the question was originally asked in 2012.

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Matt Kindig
Matt Kindig on 12 Apr 2012
You could do something like this:
a=[1 2 3;4 5 6;7 8 9;NaN NaN NaN];
a= sort(a,1,'descend');
in = any( isnan(a),2);
a = [ a(~in,:); a(in,:)];

Kye Taylor
Kye Taylor on 12 Apr 2012
This will work
newA = a; % copy original matrix
isANanRow = any(isnan(a),2); % find rows that have a nan in them
% move those nan rows to the end
newA(end-nnz(isANanRow)+1:end,:) = a(isANanRow,:);
% sort nonnan rows and place at top of newA array
newA(1:nnz(~isANanRow),:) = sort(a(~isANanRow,:),1,'descend');

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