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MathGroup Archive 1999

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Re: Lists to mask other lists

  • To: mathgroup at
  • Subject: [mg19073] Re: Lists to mask other lists
  • From: "David Bailey" <db at>
  • Date: Thu, 5 Aug 1999 01:34:58 -0400
  • Organization: University of Salford, Salford, Manchester, UK
  • References: <7o5hi2$>
  • Sender: owner-wri-mathgroup at

aram schiffman <aram at> wrote in message
news:7o5hi2$rkt at
> Howdy.
> I am trying to use one list to control the content of a second list.
> (It's not really masking, but...)
> Here's what I mean. Let's say
> maskList={1,0,0,1,1}
> realDealList={aaa,bbb,ccc,ddd,eee}
> (* could be filled with anything; same # elements as maskList }
> If a 1 appears at position n of maskList, then I leave the corresponding
> element of realDealList alone. But if a 0 appears, then I want to change
> the corresponding element of realDealList in some prescribed way. Let's
> say I change those elements to my first name (aram). Then realDealList
> would become
> {aaa,aram,aram,ddd,eee}
> I can do this in a loop, which is a really clunky solution, but isn't
> there a way I can Map across my list somehow?

MapThread is the answer because it lets your function operate on
corresponding elements from several lists:

MapThread[If[#  != 1, aram, #2] &, {maskList, realDealList}]

David Bailey
Salford Software

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