[R] Passing a Data Frame Name as a Variable in a Function

[Chel Hee Lee]

I like Jeff's comments on the previous post.

Regarding Alan's question, please see the following example.

 > df.1 <- data.frame(v1=1:5, v2=letters[1:5])
 > df.2 <- data.frame(v1=LETTERS[1:3], v2=11:13)
 > DFName <- ls(pattern = glob2rx("df.*"))[1]
 > DFName
[1] "df.1"
 > length(DFName[,1])
Error in DFName[, 1] : incorrect number of dimensions

'DFName' is a character vector of length 1 (it is neither a matrix nor a 
data frame).  In this case, you may try 'eval()' as below:

 > eval(parse(text=DFName))
   v1 v2
1  1  a
2  2  b
3  3  c
4  4  d
5  5  e
 > eval(parse(text=DFName))[,1]
[1] 1 2 3 4 5
 > length(eval(parse(text=DFName))[,1])
[1] 5
 >

Is this what you are looking for?  I hope this helps.

Chel Hee Lee


On 1/29/2015 12:34 AM, Jeff Newmiller wrote:
> This approach is fraught with dangers.
>
> I recommend that you put all of those data frames into a list and have your function accept the list and the name and use the list indexing operator mylist[[DFName]] to refer to it. Having functions that go fishing around in the global environment will be hard to maintain at best, and buggy at worst.
>
> That said, I usually work with all of my data frames combined as one and use the plyr, dplyr, or data.table packages to apply my algorithms to each group of rows identified by a character or factor column.
> ---------------------------------------------------------------------------
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> Sent from my phone. Please excuse my brevity.
>
> On January 28, 2015 5:37:34 PM PST, Alan Yong <alanyong at caltech.edu> wrote:
>> Dear R-help,
>> I have df.1001 as a data frame with rows & columns of values.
>>
>> I also have other data frames named similarly, i.e., df.*.
>>
>> I used DFName from:
>>
>> DFName <- ls(pattern = glob2rx("df.*"))[1]
>>
>> & would like to pass on DFName to another function, like:
>>
>> length(DFName[, 1])
>>
>> however, when I run:
>>
>>> length(DFName[, 1])
>> Error in DFName[, 1] : incorrect number of dimensions
>>
>> and
>>
>> length(df.1001[, 1])
>> [1] 104
>>
>> do not provide the same expected answer.
>>
>> How can I successfully pass the data frame name of df.1001 as a
>> variable named DFName in a function?
>>
>> Thanks,
>> Alan
>>
>> ______________________________________________
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>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>