Thank you, David. I believe you have made the thing more clear to me.
Best Regards,
Xie YM
在 2013-02-06 16:14:18，"David Winsemius" <dwinsem...@comcast.net> 写道：
>
>On Feb 5, 2013, at 10:48 PM, 谢一鸣 wrote:
>
>> 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?
>>
>
>I wouldn't consider that to be "computing on the language. There is an
>entire Section 6 regarding "computing on the Language". I don't see
>evidence that you have read it yet. "Computing on the language"
>generally refers to manipulation objects of 'language' class before
>they get evaluated.
>
>--
>David.
>
>> 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
>>>
>
>David Winsemius, MD
>Alameda, CA, USA
>
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