bar(data.Year(1),[data.SP500(1) data.EM(1)])
You're concatenating [data.SP500(1) data.EM(1)] as row vector so its length is 2 and you've only got one X point so the lengths aren't commensurate as the error says.
|bar| has specific input requirements for |X,Y| as noted for the |X| variable input--
"x values, specified as a vector or a matrix. If x and y are both vectors, then they must be equal length. If x and y are both matrices, then they must be equal size. If x is a vector and y is a matrix, then the length of x must equal the number of rows in y."
Not sure what your expected chart is to look like??? Where are the two values to be with respect to the one X?
ADDENDUM
It does seem to be a bug that the input parser won't accept a one-group 'grouped' input. It came to me somewhat later that must be the effect wanted but thought I'd wait for confirmation.
Only way I've been able to work around is to augment the input array with a second row of NaN elements that don't plot.
bar([data.Year(1);nan],[data.SP500(1) data.EM(1);[nan nan]])
This is a pain, agreed and worthy of an official bug report to TMW.
Interestingly, looking at the source while it's been updated significantly, the routine goes back to C Moler 1986 and looks as though this has been a limitation from the beginning.
