On 12/26/06, Alan Gauld <[EMAIL PROTECTED]> wrote: > > "linda.s" <[EMAIL PROTECTED]> wrote > > >>>> a > > array([[ 0., 1., 2., 3., 4., 5.], > > [ 6., 7., 8., 9., 10., 11.], > > [ 12., 13., 14., 15., 16., 17.], > > [ 18., 19., 20., 21., 22., 23.], > > [ 24., 25., 26., 27., 28., 29.]]) > > OK, This sets up your test array. > > >>>> a[1:3,:-1:2] # a[i,j] for i=1,2 and j=0,2,4 > > And this passes two slices. > The first is 1:3 which means 1,2 - normal slice behaviour > he second is :-1:2 which uses extended slice syntax to > specify a stepsize. So the slice says go from 0 (default) > to the last element(-1) using a step sizeof 2, which is 0,2,4 > > So we extract the 0,2,4 elements from rows 1,2 to get: > > > array([[ 6., 8., 10.], > > [ 12., 14., 16.]]) > > >>>> a[::3,2:-1:2] # a[i,j] for i=0,3 and j=2,4 > > Similarly the first slice here is the whole array(:) with a > step size of 3, thus 0,3 > The second slice is 2:-1:2 which means in practice start > at 2 and go to the end stepping in 2s, which is: 2,4 > So this time we take the 2,4 index items from rows 0,3 > which is: > > > array([[ 2., 4.], > > [ 20., 22.]]) > > Its just normal slicing notation but with a pair of them > inside the brackets instead of one. > > Which module are you using that supports this? > I've never seen it before.
It is from Hans' Book 'Python Scripting for Computational Science'. He uses Numpy: Numeric _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
