Thank you all for your replies. I had the matrix concept in mind such as explained in the numpy example.
Rob On Thu, Apr 18, 2013 at 3:19 PM, Wolfgang Maier < wolfgang.ma...@biologie.uni-freiburg.de> wrote: > Robrecht W. Uyttenhove <ruyttenhove <at> gmail.com> writes: > > > > > Hello, > > I tried out the following > code:y=[range(0,7),range(7,14),range(14,21),range(21,28),range(28,35)] > > >>> y[[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, 30, 31, 32, 33, 34]] > > >>> y[1:5:2][::3] > > [[7, 8, 9, 10, 11, 12, 13]] > > I expected the 2D list:[[ 7, 10, 13], > > [21, 24, 27]] > > > > Any ideas? > > > > Thanks, > > Rob > > PS: I used Python 2.7.3 > > > > The explanation is rather simple, just break up your complex slicing into > its parts: > y[1:5:2] => [[7, 8, 9, 10, 11, 12, 13],[21, 22, 23, 24, 25, 26, 27]] > and [::3] is asking for the first,4th,7th,... element from this list. > Obviously, only the first one's existing, so [7, 8, 9, 10, 11, 12, 13] > > What you expected is kind of vertical slicing through the rows. I don't > think you can achieve this with slicing alone in standard Python, but it's > possible with numpy arrays. > In Python you will have to combine slicing with a comprehension, like this: > [x[::3] for x in y[1:5:2]] > > Best, > Wolfgang > > -- > http://mail.python.org/mailman/listinfo/python-list > -- --------------------------------------------------------------- Wim R. Cardoen, PhD Staff Scientist, Center for High Performance Computing University of Utah (801)971-4184 *μὴ μου τοὺς κύκλους τάραττε! (Ἀρχιμήδης)* ---------------------------------------------------------------
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