Re: conditionnal rule
- To: mathgroup at smc.vnet.net
- Subject: [mg51515] Re: [mg51499] conditionnal rule
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Thu, 21 Oct 2004 22:20:18 -0400 (EDT)
- References: <200410200521.BAA08454@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On 20 Oct 2004, at 14:21, Wishmaster7 wrote:
>
> hi all !!
>
> I want to apply a rule under a certain condition. here is the example :
>
> myList = {{a, b}, {c, d}};
>
> myList //. {a,x_}->{a,d}
>
> apply this rule if Length[x]===1 (this means that x can not be a list)
>
> I tried something like :
>
> myList //. {a_,x_}->{c,d}/;Length[x]===1
>
> or
>
> myList //. {a_,x_?Length[x]===1}->{c,d}/
>
> but it does not work.
>
> can someone help me ?
>
>
Surely, you must have meant Length[x] == 0 not Length[x] == 1 ?
You do not need to use ReplaceRepeated here but you do need to use
RuleDelayed instead of Rule:
myList = {{a, b}, {c, d}};
myList /. {a_, x_} :> {c, d} /; Length[x] == 0
{{c, d}, {c, d}}
Andrzej Kozlowski
Chiba, Japan
http://www.akikoz.net/~andrzej/
http://www.mimuw.edu.pl/~akoz/
- References:
- conditionnal rule
- From: darkness_wizard@hotmail.com (Wishmaster7)
- conditionnal rule