How do I pull data from two different matrices to form a new matrix?

Hi,

I have two different 30 x 10 matrixes (d1 and d2) that I am trying to pull rows from and only want a specific row from each of them to form a new matrix. The rows that I want are specified in another 30x1 matrix (I) with values of only 1's and 2's depicting the matrix I need to pull from.

I know i could pull one row of a specified matrix with the following command:

dtest=d1(I(1),:)

Unfortunately, I want to use my I matrix to select d1 or d2 in the above command.

Answer 1

[Walter Roberson]

d12 = cat(3, d1, d2);

[r, c] = size(d1);
dtest = d12( sub2ind(size(d12),repmat((1:r).',1,c),repmat(1:c,r,1),repmat(I,1,c)) );

Answer 2

[Roger Stafford]

   p = repmat(I==1,1,10);    <-- Corrected
   D = p.*D1+(1-p).*D2; % <-- The desired result

[Walter Roberson]

I think your repmat() is off there; with a single count you are asking for repeating 10 horizontally and 10 vertically.

[Roger Stafford]

Oops, you're right Walter. It should be

   p = repmat(I==1,1,10);