Re: ReplacePart in an If[] construct?
- To: mathgroup at smc.vnet.net
- Subject: [mg67819] Re: [mg67816] ReplacePart in an If[] construct?
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Sun, 9 Jul 2006 04:50:37 -0400 (EDT)
- References: <200607080857.EAA20495@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On 8 Jul 2006, at 09:57, gardyloo wrote:
>
> 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.
They are indeed both "replaced", but only the second one is RETURNED.
Note that ReplacePart does not change its first argument:
a= {4, another, example, list};
ReplacePart[a,replaced!,3]
{4,another,replaced!,list}
a
{4,another,example,list}
Andrzej Kozlowski
Oxford, UK
- References:
- ReplacePart in an If[] construct?
- From: gardyloo <gardyloo@mail.wsu.edu>
- ReplacePart in an If[] construct?