[R] name of a name

[David Winsemius]

On Nov 19, 2009, at 4:39 AM, baptiste auguie wrote:

> Hi,
>
> Try this,
>
>
> d <- data.frame(a=1:4, b=3:6)
>
> var <- "a"
>
> mean(d[var])

I tried get() on Simpson's pasted argument without success. Assuming  
the OP still wanted to use only text arguments, then this approach works

dfn <- "d"

get(dfn)[var]

So get() works only on complete objects and not on expressions that  
include extraction operations.


>
> ## or, if you are not aware of
> ## fortune("parse")
>
> xx <- paste("d$",var, sep="")
> mean(eval(parse(text=xx)))
>
> HTH,
>
> baptiste
>
>
>
>
> 2009/11/19 William Simpson <william.a.simpson at gmail.com>:
>> I have quite a complicated problem that's hard to describe.
>>
>> Suppose I have a dataframe d. I want to access the vector d$var,  
>> where
>> var is one of the variables in d. Just take for granted that  
>> there's a
>> good reason I want to do this as follows.
>>
>> var<-"DeOxyA"
>> xx<-paste("d$",var, sep="")
>> mean(xx)
>> [1] NA
>> Warning message:
>> In mean.default(xx) : argument is not numeric or logical: returning  
>> NA
>>
>>> mean(d$DeOxyA)
>> [1] 21.98904
>>
>> How can I convert xx so I can do mean(xx), for example? Currently xx
>> is a character, not a variable.
>> as.numeric doesn't do it. I want R to see
>> mean(DeOxyA), not
>> mean("DeOxyA")
>>
>> I'm stumped.
>>
>> Thanks very much for any help.
>>
>> Bill
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT