Re: Previous variable affects "/."
- To: mathgroup@smc.vnet.net
- Subject: [mg11313] Re: [mg11236] Previous variable affects "/."
- From: Bob Hanlon <BobHanlon@aol.com>
- Date: Wed, 4 Mar 1998 01:40:16 -0500
You need to use RuleDelayed:
a = {{1, 2}, {3, 4}, {5, 6}, {7, 8}}; a /. {x_, y_} -> {x}
{{7},{7},{7},{7}}
x = 7;
a /. {x_, y_} -> {x}
a /. {x_, y_} :> {x}
{{7},{7},{7},{7}}
{{1},{3},{5},{7}}
?Rule
"lhs -> rhs represents a rule that transforms lhs to rhs."
?RuleDelayed
"lhs :> rhs represents a rule that transforms lhs to rhs, evaluating rhs
only \
when the rule is used."
Bob Hanlon