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conditionnal rule

• To: mathgroup at smc.vnet.net
• Subject: [mg51499] conditionnal rule
• From: darkness_wizard at hotmail.com (Wishmaster7)
• Date: Wed, 20 Oct 2004 01:21:19 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

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 ?

• Follow-Ups:
  • Re: conditionnal rule
    • From: Tomas Garza <tgarza01@prodigy.net.mx>
  • Re: conditionnal rule
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>