[R] how to check if an attribute exists

[Nick Matzke]

I am dealing with an object that sometimes has a certain 
attribute, sometimes doesn't.  How do I check for this? 
"exists" doesn't work...

=======================
 > z=c()
 > z$a = c("c", "d", "f")
 > z
$a
[1] "c" "d" "f"

 > exists("z")
[1] TRUE

 > exists("z$a")
[1] FALSE
=======================

...basically, I want something that returns TRUE if the $a 
exists in z...

Thanks!
Nick



-- 
====================================================
Nicholas J. Matzke
Ph.D. Candidate, Graduate Student Researcher

Huelsenbeck Lab
Center for Theoretical Evolutionary Genomics
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Department of Integrative Biology
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