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Transforming/expanding a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg127970] Transforming/expanding a list
  • From: Mark Coleman <markspcoleman at gmail.com>
  • Date: Thu, 6 Sep 2012 04:14:14 -0400 (EDT)
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  • Delivered-to: l-mathgroup@wolfram.com
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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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