[R] Getting at what a named object represents in a function...

[Martin Waller]

Hi,

I'm pretty new to R.

I have an object (say a list) and I I have a function that I call on 
various columns in that list (excuse terminology if it's wrong/ambiguous).

Imagine its like this (actual values are unimportant) and called mylist:

 >mylist
A    B
1    5
2    5
3    6  4    8
5    0

I have a function:

foo = function(param){
 #modify list A or B values depending on whether A or B's passsd in (via 
'param')
   param[someindex]=another_value #doesn't change value in lits$A or 
list$B (whichever's been passed in as 'param')
#I want something like:
 #if 'param' is list$A then list$A[someindex]=another_value
 #else if 'param' is list$B then list$B[some_index] = another_value
}

I then call this function on mylist$A (i.e. foo(mylist$A) and then on 
mylist$B (i.e. foo(mylist$B))

so 'param' in function foo is either mylist$A or mylist$B - can I tell 
which it is so that when param[someindex] is changed, it's actually 
mylist$A or mylist$B that's changed?

If I modify param values in foo(), they're not modified in list...so is 
there a way to tell whether param represents list$A or list$B and hence 
allow to me to modify those actual values rather than 'param'?

Thanks for help,

Martin