This seems to be a very common problem of mine:

data = [1 2 3; 4 5 6];
mask = [true false true];

mask = repmat(mask, 2, 1);

data(mask) ==> [1; 4; 3; 6]

What I wanted was [1 3; 4 6].

Yes I can just reshape it to the right size, but that seems the wrong way to do it. Is there a better way? Why doesn't data(mask) return a matrix when it is actually rectangular? I understand in the general case it may not be, but in my case since my original mask is an array it always will be.

Corollary

Thanks for the answer, I just also wanted to point out this also works with anything that returns a numeric index like ismember, sort, or unique.

I used to take the second return value from sort and apply it to every column manually when you can use this notion to do it one shot.