How to output both rho and pvalues of the Corr function when having an iterative loop

Hi, I can't seem to get around how to do this. I have 12xm matrix (a1) of which I want to calculate the linear rank correlation rho an pvalues (using Corr function and pearson correlation type) from paired columns vectors, i.e. between 6 rows in each column and the next 6 rows in that column (these are replicate measurements, designated rep1 and rep2, respectively), and I want to iterate that with a for loop for all the m columns in the matrix a1.

I have it working so that it spits out the rho values in a 1xm vector, but I don't know how to get the script to do that also for the p-values associated with each correlation.

this is the script I have:

            results=zeros(1,size(a1,2));
              rep1=a1(1:6,1:size(a1,2));
              rep2=a1(7:12,1:size(a1,2));

                  for repit = 1:size(a1,2);
                    results(repit) =  corr(rep1(:,repit),rep2(:,repit));
                          end

I know that [r,p] = corr(x,y) gives me both the r and p-value, but how do I build this into the iterative loop that I have going so that it does that for each each two column vectors in every columns of the a1 matrix.....?

I hope I am making this clear enough... otherwise, don't bother asking for clarifications.

Thank you.

Answer 1

[Mischa Kim]

Fly, you could use a cell array:

 ...
 [r{repit} p{repit}] = corr(rep1(:,repit),rep2(:,repit));
 ...

The results from the first iteration are then accessed via r{1} and p{1}, from the second in r{2}...

If the r- and p-values are scalars, you can also just use simple numeric arrays:

 [r(repit) p(repit)] = corr(rep1(:,repit),rep2(:,repit));

The advantage of cell arrays for non-scalars is that you don't need to worry about matrix dimensions.

[Fly Haynes]

Thanks!!