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Re: Transforming/expanding a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg127977] Re: Transforming/expanding a list
  • From: Adriano Pascoletti <adriano.pascoletti at uniud.it>
  • Date: Fri, 7 Sep 2012 04:54:09 -0400 (EDT)
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  • References: <20120906081415.0241D684C@smc.vnet.net>

In[1]:= (If[#1 =!= NULL, save = #1, save] & ) /@ {x1, NULL, NULL, x2, NULL,
NULL,  NULL, NULL,  x3, NULL, NULL, x4, x5, NULL}
Out[1]= {x1, x1, x1, x2, x2, x2, x2, x2, x3, x3, x3, x4, x5, x5}


Adriano Pascoletti

2012/9/6 Mark Coleman <markspcoleman at gmail.com>

> 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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