On Feb 5, 2013, at 8:07 PM, 谢一鸣 wrote:
Dear ALL,
I need a function that takes character string as argument value and
replaces corresponding argument( which is behind dollar sign "$") in
function body with its value.
For example:
function(dataframe, argument="ANYTHING I WANT")
{
return(dataframe$argument)
}
Even though I know there must be lots of possible alternative ways
to do this, I really want to do the job just like the form in the
above example and which I believe that has a close connection with
"Programming on language" style(I read the term on some guides but
really got no clue whether I refer to it here in a right way).
Anyone who happens to know the method or the mechanism please kindly
let me know. Thank you very much, and please reply in very simple
English, because i am a poor English user.
The "$" construction is only a syntactic shortcut for "[["argument"]].
What you are looking for is described in the ?"[[" page. You should be
constructing a formal that is assigned a syntactically legal column
name ... NOT "ANYTHING I WANT". Perhaps:
function(dfrm , colname = "V1") {
return( dfrm[[ colname ]] )
# the argument will get evaluated as "V1" unless an alternate colname
argument is supplied
}
( You can't get "$" to evaluate a character column name.)
--
David Winsemius, MD
Alameda, CA, USA
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