Hi:

David explained the quoting issue well. My question is: what type of output
do you want from the function? Using David's fix, I get

learnfn <- function(data,column) {
print(data)
data[, column]
}

The idea is to leave the column unquoted in the body of the function and to
quote it in the function call, as in

learnfn(data, 'x')
    x         y  z
1   1 0.6651562 11
2   2 2.9268958 12
3   3 3.9521160 13
4   4 4.6214315 14
5   5 7.4039838 15
6   6 5.7174185 16
7   7 7.7249067 17
8   8 6.9924741 18
9   9 7.4228238 19
10 10 9.4208857 20
 [1]  1  2  3  4  5  6  7  8  9 10

After printing the data frame, the return value is a vector. I would expect
that one might prefer a data frame instead. If so, you need to modify the
return to

learnfn <- function(data,column) {
print(data)
data[, column, drop = FALSE]
}

> learnfn(data, 'x')
    x         y  z
1   1 0.6651562 11
2   2 2.9268958 12
3   3 3.9521160 13
4   4 4.6214315 14
5   5 7.4039838 15
6   6 5.7174185 16
7   7 7.7249067 17
8   8 6.9924741 18
9   9 7.4228238 19
10 10 9.4208857 20
    x
1   1
2   2
3   3
4   4
5   5
6   6
7   7
8   8
9   9
10 10


On Fri, Dec 24, 2010 at 1:29 PM, John Sorkin <jsorkin@grecc.umaryland.edu>wrote:

> I am trying to learn more about how to write functions. I would like to
> pass a data frame (or matrix)  and depending on the parameters passed to the
> function work with a given column of the data frame or matrix. My function,
> learnfn is given below as are two calls to the function. The first call is
> an attempt to print the x column from the data frame, the second call is an
> attempt to print the y column. I hope someone can modify my function so it
> works.
> Thank you,
> John
>
>  # create data frame
> x<-1:10
> y <- x+rnorm(10)
> z <- 11:20
> data <- data.frame(x,y,z)
> data
>
>
> learnfn <- function(data,column) {
> print(data)
> data[,"column"]
> }
>
> # work on the "x" column
> learnfn(data,x)
>
> # work on the "y" column
> learnfn(data,y)
>
>
> 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 ...{{dropped:13}}

