Ignore NaN values when sorting

Good afternoon everybody!

I have a matrix of the type:

A = [10 NaN 20 NaN]

and I want to put a rank in ascending order to these values but, if there is a NaN value, it is ignored or set equal to 0.

For instance, the result can be:

rank = [1 0 2 0]

It would be awesome if you can help me with this enigma.

Thank you!

Answer 1

[Walter Roberson]

validmask = ~isnan(A);
[~, nonnanrank] = sort(A(validmask));
rank = zeros(size(A));
rank(validmask) = nonnanrank;

However I recommand that you use a different variable name rather than rank to avoid interfering with using the MATLAB function rank() . rank() is used less frequently than sum() or length() are, so this is perhaps less of an issue than using those variables would be.

[Marco Sartori]

That worked perfectly. Thank you very much for your help and promptness!

[Marco Sartori]

At the same time, what if i'm working with a matrix instead of the simple vector above?

the process would be something like this but i cannot procede by specifing A(validmask(i,:)) for A(i,:)

ranks = zeros(size(A));
for i = 1:t
    validmask(i,:) = ~isnan(A(i,:));
    ?
    ?
end

[Walter Roberson]

The easiest way would probably be to work column by column.

I can think of a vectorized algorithm, but it involves some sub2ind() tricks that are less than clear to read. Sometimes it just isn't worth doing unless your arrays are large enough that performance gets really important but at the same time not so large that the extra memory needed for vectorization is not a factor.

Answer 2

[madhan ravi]

[~, where] = sort(A);
Wanted = where .* ~isnan(A)