Easy! a[b==i] --bb On 4/24/07, Tommy Grav <tgrav at cfa.harvard.edu> wrote: > I have two arrays: > > a = numpy.array([0,1,2,3,4,5,6,7,8,9]) > b = numpy.array([0,0,1,1,2,2,0,1,2,3]) > > I would like to get the part of a that corresponds > to where b is equal to i. > > For example: > > i = 0 => ([0,1,6]) > i = 1 => ([2,3,7]) >