in Matlab, matrix indices start from one, not zero like other programming languages, but your index starts from zero:
so what you are actually doing is this:
I guess what you did try to do is more like copy the entire row of data_in_temp into the i'th row of data_out?
if so, try this:
data_out(i,:) = data_in_temp
or if you are trying to copy a subset of that row, make sure the index of data_in_temp is the same size as that of data_out