"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. HTH, -- Alan Gauld Author of the Learn to Program web site http://www.freenetpages.co.uk/hp/alan.gauld _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
