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Re: Transforming/expanding a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg128017] Re: Transforming/expanding a list
  • From: Dana DeLouis <dana01 at me.com>
  • Date: Sun, 9 Sep 2012 05:09:26 -0400 (EDT)
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> real numbers, separating some number of Strings

Hi.  If it's really just any String, perhaps another idea:

v={1,2,"Null", 3,"Null2", "Null3",4,5,"Null4",6};

FoldList[If[StringQ[#2],#1,#2]&, First[v], Rest[v]]

{1,2,2,3,3,3,4,5,5,6}

= = = = = = = = = =
HTH  :>)
Dana DeLouis
Mac & Mathematica 8
= = = = = = = = = =



On Thursday, September 6, 2012 4:15:28 AM UTC-4, Mark Coleman wrote:
> I'm working on some Mathematica code that will help transform a large set of lists drawn from my company's legacy database systems. A typical row of the raw data looks like
> 
> {x1,NULL,NULL,x2,NULL,NULL,NULL,NULL,x3,NULL,NULL,x4,x5,NULL} ...
> 
> The lists are sequences of real numbers, separating some some number of Strings which for convenicence sake we call "NULL" (as opposed to a proper Mathematica Null). The goal is to create a new list where each NULL is replaced by the real number that most recently proceeds it (note that any number of NULLs may occur before or after any real values). I would like the code to return
> 
> {x1,x1,x1,x2,x2,x2,x2,x2,x3,x3,x3,x4,x5,x5}
> 
> 
> Thanks
> Mark




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