Move all NaN to end of matrix columns.

Hi!

I have a 3D matrix of many rows. At som places there is NaN values in the middle of some rows that I don't want there, ex:

A(:,:,1) = [8 8; 9 9; 8 8; 9 9; NaN NaN; 1 1; 2 2; 3 3; 5 5; 7 7];

A(:,:,2) = [2 2; 3 3; 4 4; NaN NaN; NaN NaN; 1 2; 2 5; 3 7; 5 6; 7 8];

I want to remove the NaN's somehow. But since it is a 3D matrix it has to remain the same size and hence I can't just remove all NaN's by setting A(any(any(isnan(A),3),2),:,:) = [].

Answer 1

[Stephen23]

Without sorting the other values:

>> A(:,:,1) = [8 8; 9 9; 8 8; 9 9; NaN NaN; 1 1; 2 2; 3 3; 5 5; 7 7];
>> A(:,:,2) = [2 2; 3 3; 4 4; NaN NaN; NaN NaN; 1 2; 2 5; 3 7; 5 6; 7 8];
>> [~,idr] = sort(isnan(A),1);
>> S = size(A);
>> [~,id2,id3] = ndgrid(1:S(1),1:S(2),1:S(3));
>> idx = sub2ind(S,idr,id2,id3);
>> B = A(idx)
B(:,:,1) =
     8     8
     9     9
     8     8
     9     9
     1     1
     2     2
     3     3
     5     5
     7     7
   NaN   NaN
B(:,:,2) =
     2     2
     3     3
     4     4
     1     2
     2     5
     3     7
     5     6
     7     8
   NaN   NaN
   NaN   NaN

[Hampus Alfredsson]

Thank you @Stephen Cobeldick. Works perfectly.

[Bryan]

Hi Stephen,

Found this question a few months ago when I had the same problem as Hampus describes.

Ingenious, superfast solution. Thanks very much.

Regards,

Bryan

[Stephen23]

@Bryan: if you like it then you can give it a vote :)

[Jorge Morales]

How can you apply this to a Table??

Answer 2

[M]

if you want to move all NaN to end of matrix you can use:

sort(A)
ans(:,:,1) =

     1     1
     2     2
     3     3
     5     5
     7     7
     8     8
     8     8
     9     9
     9     9
   NaN   NaN
ans(:,:,2) =

     1     2
     2     2
     2     3
     3     4
     3     5
     4     6
     5     7
     7     8
   NaN   NaN
   NaN   NaN

[Hampus Alfredsson]

Yes. But I want all the other rows to remain in the same order.

Answer 3

[Jos (10584)]

10+ years ago, I submitted the function sortlind to the Matlab File Exchange, which returns linear indices (rather than sub indices as sort does). This is how it works:

[~, I] = sortlind(isnan(A)) ; 
B = A(I) ; % all NaNs of A moved to the end

sortlind can be downloaded here: https://uk.mathworks.com/matlabcentral/fileexchange/19443