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"Collapsing" a list into a list of changes

Adam Przybyla adam at gliwice.pl
Mon Feb 7 07:41:12 EST 2005 
Alan McIntyre <alan.mcintyre at esrgtech.com> wrote:
> 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?
>>> p=[1,1,1,1,1,4,4,4,8,8,9]
>>> filter(lambda y: y>0, map(lambda x,y: x==y and -1 or x,[0]+p,p+[0]))
[1, 4, 8, 9]
>>>
Z powazaniem
								Adam Przybyla
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