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MathGroup Archive 2005

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Re: Elegant syntax for multiple conditional assignment?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54410] Re: [mg54337] Elegant syntax for multiple conditional assignment?
  • From: Scott Hemphill <hemphill at hemphills.net>
  • Date: Sun, 20 Feb 2005 00:08:22 -0500 (EST)
  • Reply-to: hemphill at alumni.caltech.edu
  • Sender: owner-wri-mathgroup at wolfram.com

On Sat, 19 Feb 2005, Bob Hanlon wrote:

> old={a1,c1,x1,y1};
> 
> new={a2,c2,x2,y2};
> 
> cond={True,False,True,False};
> 
> {a,c,x,y} = If[#[[1]],#[[2]],#[[3]]]&/@
>     Transpose[{cond,new,old}]
> 
> {a2,c1,x2,y1}
> 
> {a,c,x,y} = If[#[[1]],#[[2]],#[[3]]]&/@
>     Thread[{cond,new,old}]
> 
> {a2,c1,x2,y1}

This isn't what I want.  What I want is this:

a1={1,2,3,4,5};
c1={6,7,8,9,10};
x1={11,12,13,14,15};
y1={16,17,18,19,20};

old={a1,c1,x1,y1};

a2={21,22,23,24,25};
c2={26,27,28,29,30};
x2={31,32,33,34,35};
y2={36,37,38,39,40};

new={a2,c2,x2,y2};

cond={True,False,True,False,True}  (* Note: five elements *)

What I want is code which takes old, new, and cond and makes this 
assignment:

a={21,2,23,4,25};
c={26,7,28,9,30};
x={31,12,33,14,35};
y={36,17,38,19,40};

Scott
-- 
Scott Hemphill	hemphill at alumni.caltech.edu
"This isn't flying.  This is falling, with style."  -- Buzz Lightyear


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