[R] access a column of a dataframe without qualifying the name of the column

[Bert Gunter]

?substitute

test <- function(col,frm) {
  eval(substitute(col),frm)
}

test2 <- function(col,frm){
  cname<- deparse(substitute(col))
  frm[[cname]]
}

 z <- data.frame(x=1:3,y=letters[1:3])

test(x, z)

test2(x, z)


-- Bert

On Wed, Dec 29, 2010 at 4:44 PM, David Winsemius <dwinsemius at comcast.net> wrote:
>
> On Dec 29, 2010, at 7:11 PM, John Sorkin wrote:
>
>> I am trying to write a function that will access a column of a data frame
>> without having to qualify the name of the data frame column as long as the
>> name of the dataframe is passed to the function. As can be seen from the
>> code below, my function is not working:
>
> Not sure what the verb "qualify" means in programming. Quoting?
>
>>
>> df <- data.frame(x=1:10,y=11:20)
>> df
>>
>> test <- function(column,data) {
>>  print(data$column)
>> }
>>
>> test(x,df)
>>
>> I am trying to model my function after the way that lm works where one
>> needs not qualify column names, i.e.
>
>
>> df <- data.frame(x=1:10,y=11:20)
>> test <- function(column,dat) { print(colname <-
>> deparse(substitute(column)))
> +  dat[[colname]]
> + }
>>
>> test(x,df)
> [1] "x"
>  [1]  1  2  3  4  5  6  7  8  9 10
>>
>
> --
> David.
>
>
>>
>>
>> fit1<- lm(y~x,data=df)
>>
>>
>> John David Sorkin M.D., Ph.D.
>> Chief, Biostatistics and Informatics
>> University of Maryland School of Medicine Division of Gerontology
>> Baltimore VA Medical Center
>> 10 North Greene Street
>> GRECC (BT/18/GR)
>> Baltimore, MD 21201-1524
>> (Phone) 410-605-7119
>> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>>
>> Confidentiality Statement:
>> This email message, including any attachments, is for th...{{dropped:6}}
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
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>> 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
> West Hartford, CT
>
> ______________________________________________
> 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.
>



-- 
Bert Gunter
Genentech Nonclinical Biostatistics