Thanks David, your solution perfectly solve my problem. But Do you know what
exactly the mechanism of "Computing on the language" in pdf file: "R language
definition", Can that "THING" do the same job?
Thank you very much!
Xie YM
2013-02-06 14:22:57，"David Winsemius" <dwinsem...@comcast.net> 写道：
>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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