# Sorting NaN

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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

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

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')
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.

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 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');