>Psychtoolbox>PsychProbability

sel = RandSel(in,n)
if N is a scalar
randomly selects N elements from set IN, each element from IN will
be selected up to one time (so sampling without replacing).
Output is of size 1xN
if N is a vector
randomly selects prod(N) elements from set IN, without replacing. N
specifies the shape of the output, e.g., if N=[10 10 5], SEL will be
a 10x10x5 matrix
IN can be of any datatype and can have any number of dimensions and
elements