[R] name of a name

William Simpson william.a.simpson at gmail.com
Thu Nov 19 12:01:05 CET 2009


Thanks very much Phil and Baptiste!
d[[var]]
is exactly what I wanted.
Sorry for being so inarticulate. I still couldn't describe my problem
if I wanted to! Anyway, now I have the solution.

Cheers
Bill

On Thu, Nov 19, 2009 at 9:39 AM, baptiste auguie
<baptiste.auguie at googlemail.com> wrote:
> Hi,
>
> Try this,
>
>
> d <- data.frame(a=1:4, b=3:6)
>
> var <- "a"
>
> mean(d[var])
>
> ## 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.
>>
>




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