Thanks to everyone for the answers. I'll definitely check Numeric Python.
Cheers Bernard On 11/16/05, Danny Yoo <[EMAIL PROTECTED]> wrote: > > > On Wed, 16 Nov 2005, Bernard Lebel wrote: > > > Let say I have a list of lists. Each individual lists have a bunch of > > elements. Now I would like to either get or set the first element of > > each individual list. I could do a loop and/or list comprehension, but I > > was wondering if it was possible with something like: > > > > aList = [ [1,1,1], [2,2,2,], [3,3,3] ] > > aList[:][0] = 10 > > > Hi Bernard, > > I think I see what you're trying to do; you're trying to clear the first > column of each row in your matrix. Unfortunately, this is not done so > easily in standard Python. However, if you use the third-party Numeric > Python (numarray) package, you can use its array type to do what you want. > > > > If I print aList[:], I get the list with the nested sublists. > > > > >>> aList[:] > > [[1, 1, 1], [2, 2, 2], [3, 3, 3]] > > Yes, sounds good so far. > > > > But as soon as I introduce the [0], in an attempt to access the first > > element of each sublist, I get the first sublist in its entirety: > > > > >>> aList[:][0] > > [1, 1, 1] > > > Let's do a quick substitution model thing here. You mentioned earlier > that: > > > >>> aList[:] > > [[1, 1, 1], [2, 2, 2], [3, 3, 3]] > > So if we just plug that value into aList[:][0]: > > aList[:][0] ==> [[1, 1, 1,], [2, 2, 2], [3, 3, 3]] [0] > > then we see that we're just asking for the first element of aList[:], > which is [1, 1, 1]. > > > > > I would have hoped to get something like [1, 2, 3] > > Take a look into Numeric Python: it'll give you the row/column slicing > operations that you're expecting. As a concrete example: > > ###### > >>> import numarray > >>> a = numarray.array([[1, 2, 3], > ... [4, 5, 6], > ... [7, 8, 9]]) > >>> a[:, 0] > array([1, 4, 7]) > >>> a[:, 1] > array([2, 5, 8]) > >>> a[:, 2] > array([3, 6, 9]) > ###### > > > Best of wishes! > > _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor