William Stein wrote: > On 10/26/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: >>> which produces a nested list. Is there a way to flatten the list by one >>> or two levels, but not flatten it all the way? Something like: >>> >>> sage: flatten([[[1,2],[3,4]],[[5,6],[7,8]]],1) >>> [[1,2],[3,4],[5,6],[7,8]] > > An easy way to do the above is the following: > > sage: v = [[[1,2],[3,4]],[[5,6],[7,8]]] > sage: sum(v, []) > [[1, 2], [3, 4], [5, 6], [7, 8]] > sage: sum(sum(v, []), []) > [1, 2, 3, 4, 5, 6, 7, 8] > > This is not a flatten-to-level 1 in general, but if you really want > to do just things like the example above it does what you want. > > William > > > >
I've modified the flatten.py function to deal with a max level of flatten. It runs a little slower than the current flatten function (220 microseconds instead of 170 microseconds on %timeit for a particular case), but I think the extra functionality is worth it. If the time issue is a problem, we can just split the function into two branches depending on if a max_level is passed to the function. I posted up the patch on ticket #1016. I'm very curious how this compares to a recursive version. The recursive version noted above and William's version using sum both choke when the depth of the list is not uniform (e.g., [[1,[2]],[3,4]] ). With the patched version of flatten, you can restrict the flattening based on both the types of elements and the level at which the elements are located in the nested list. Thanks, Jason --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
