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MathGroup Archive 2007

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Re: Partition a list into sublists of unequal size

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83933] Re: [mg83919] Partition a list into sublists of unequal size
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Wed, 5 Dec 2007 07:04:20 -0500 (EST)
  • References: <200712040929.EAA17852@smc.vnet.net>

On Dec 4, 2007, at 4:29 AM, antf wrote:

> Hello,
>
> I have a list that looks like the following:
>
> list={1,0,0,1,0,0,1,1,0,1,0,0,0,0,1,0}
>
> I then find the positions of the 1s in the list:
>
> positions = Flatten@Position[list,1]
>
> {1,4,7,8,10,15}
>
> I then want to partition a third list into sublists so that the first
> sublist is from index 1;;1, the second sublist is from index 2;;4, the
> third sublist is from index 5;;7, the fourth sublist is just element
> 8, etc.
>
> Currently, I use Partition on the positions sublist with overlap as
> in:
>
> Partition[Join[{1},positions],2,1]
>
> {{1,1},{1,4},{4,7},{7,8},{8,10},{10,15}}
>
> I then use this list to partition the target list by Mapping Take to
> each element of this list and adjusting the first index appropriately.
>
> I am sure there must be a simpler way to do this.  Can anyone tell me
> how to do this operation?

I'm not sure about simple, but here's my approach

list[[Range[#[[1]]+1,#[[2]]]]]]&/@Partition[Prepend[positions,0],2,1]

Regards,

Ssezi


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