"Collapsing" a list into a list of changes

[Coates, Steve (ACHE)]

It's not _exactly_ what you asked for but it may be enough...

Python 2.4 (#60, Nov 30 2004, 11:49:19) [MSC v.1310 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from sets import Set
>>> l = [0,0,1,1,1,2,2,3,3,3,2,2,2,4,4,4,5]
>>> s = Set(l)
>>> s
Set([0, 1, 2, 3, 4, 5])
>>> l2 = list(s)
>>> l2
[0, 1, 2, 3, 4, 5]
>>>

I say it's not exactly what you wanted because I don't think the
ordering
of l2 is necessarily the same as l. That may or may not be a problem for
you.

Regards
Steve



> -----Original Message-----
> From: Alan McIntyre [mailto:alan.mcintyre at esrgtech.com]

> Sent: 04 February 2005 17:44
> To: python-list at python.org
> Subject: "Collapsing" a list into a list of changes
>

> Hi all,
>

> I have a list of items that has contiguous repetitions of

> values, but the number and location of the repetitions is not

> important, so I just need to strip them out.  For example, if

> my original list is [0,0,1,1,1,2,2,3,3,3,2,2,2,4,4,4,5], I

> want to end up with [0,1,2,3,2,4,5].
>

> Here is the way I'm doing this now:
>

> def straightforward_collapse(myList):
>      collapsed = [myList[0]]
>      for n in myList[1:]:
>          if n != collapsed[-1]:
>              collapsed.append(n)
>

>      return collapsed
>

> Is there an elegant way to do this, or should I just stick

> with the code above?
>

> Thanks,
> Alan McIntyre
> http://www.esrgtech.com
>

>


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