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Re: Transforming/expanding a list

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  • Subject: [mg127993] Re: Transforming/expanding a list
  • From: Bob Hanlon <hanlonr357 at>
  • Date: Fri, 7 Sep 2012 04:59:30 -0400 (EDT)
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list = {x1, "NULL", "NULL", x2, "NULL", "NULL", "NULL", "NULL", x3,
   "NULL", "NULL", x4, x5, "NULL"};

list //. {s__, str_String, r___} :> {s, Last[{s}], r}

{x1, x1, x1, x2, x2, x2, x2, x2, x3, x3, x3, x4, x5, x5}

Bob Hanlon

On Thu, Sep 6, 2012 at 4:14 AM, Mark Coleman <markspcoleman at> 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
> 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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