Sorting NaN

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

Answer 1

[Matt Tearle]

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

Answer 2

[Huw S]

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]

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.

Answer 3

[Matt Kindig]

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,:)];

Answer 4

[Kye Taylor]

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');