how to select element depend on text content in using xslt

[Xero852]

the source xml is like:\[code\]<source> <idset> 1,2,4 </ideset> <c id = "1">aaa</c> <c id = "2">bbb</c> <c id = "3">ccc</c> <c id = "4">ddd</c></source>\[/code\]use the idset content "1,2,4" to generate new xml, like this:\[code\]<result> aaabbbddd</result>\[/code\]i think it should use the text "1,2,4" as a parameter, but i dont know how to do this