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RE: ReplacePart in an If[] construct?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67831] RE: [mg67816] ReplacePart in an If[] construct?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sun, 9 Jul 2006 04:51:09 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Curtis,

Because the result of the first ReplacePart was thrown away and the second
ReplacePart started afresh. To replace more than one part use

testList = {{3, an, example, list},
   {4, another, example, list}};

(If[  (ListQ[#1] && First[#1] == 4),
    ReplacePart[#1, replaced!, {{2}, {3}}],
   #1      (*otherwise*)
] & ) /@ testList

{{3, an, example, list}, {4, replaced!, replaced!, list}}

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/


From: gardyloo [mailto:gardyloo at mail.wsu.edu]
To: mathgroup at smc.vnet.net


Hi, all,

   It's probably that I'm too tired, but I have a question about using
ReplacePart in an If[] construct. I've made up a (very) minimal example:

In[1]:=
testList = {{3, an, example, list},
   {4, another, example, list}}

Out[1]=
{{3, an, example, list}, {4, another, example, list}}

In[2]:=
(If[  (ListQ[#1] && First[#1] == 4),
    ReplacePart[#1, replaced!, 3];
    ReplacePart[#1, replaced!, 2],
   #1      (*otherwise*)
] & ) /@ testList

Out[2]=
{{3, an, example, list}, {4, replaced!, example, list}}


        Can someone tell me why BOTH the second and third positions in
the second element in testList aren't turned to "replaced!" ?  I have
plenty of other ways of doing this, but this seemed the most
straightforward, and I can't wrap my head around it, for some reason.



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Curtis Osterhoudt
gardyloo at mail.remove_this.wsu.and_this.edu
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