Why I think range is a wart.

[Magnus Lie Hetland]

In article <mailman.1016161825.20741.python-list at python.org>,
Christian Tanzer wrote:
>
[snip]
>> It happens to me too, mostly when I'm using a sliding window
>> type algorithm, that is, I need to look at two adjacent members
>> of the list. You can't do this easily by iterating through the list;
>> unrolling the first entry and the last entry are a pain.
>
>I use a function pairwise to do such things:
>
>    for l, r in pairwise(mylist) :
>        <whatever>
>
>Probably not as fast as index manipulation, but IMHO much easier to
>read/write/understand.

As an apropos, I need sliding windows a bit too, and have been using
the following solution in numarray:

  from numarray import *

  def windows(data, size):
      shape = (size, len(data)-size+1)
      return data[sum(indices(shape))]

It can be used like this:

  >>> print windows(arange(10), 3)
  [[0 1 2]
   [1 2 3]
   [2 3 4]
   [3 4 5]
   [4 5 6]
   [5 6 7]
   [6 7 8]
   [7 8 9]]

It took me a while to figure out exactly how to do it but figuring out
how it works shouldn't be that hard ;)

Of course these are overlapping windows (with step 1) -- a
non-overlapping version is left as an exercise for the reader <wink>.

--
Magnus Lie Hetland                                  The Anygui Project
http://hetland.org                                  http://anygui.org