[R] Symbolic references - passing variable names into functions

[Gabor Grothendieck]

Returning the changed value as in Erik's answer is probably the
most common and R-like solution but here are two others.  The
assign/get approach is perhaps the closest to what you are asking
for.

# replacement function approach

# replacement function - rhs is formula whose response is assigned to
"dataf<-" <- function(data, value) {
	v <- all.vars(value)
	data[[v[1]]] <- data[[v[2]]]
	data
}
BOD <- datasets::BOD
BOD
dataf(BOD) <- Time ~ demand
BOD

# assign/get approach

dataf <- function(data, col1, col2, env = parent.frame()) {
	data.name <- deparse(substitute(data))
	data <- get(data.name, env)
	data[col1] <- data[col2]
	assign(data.name, data, env)
}
BOD <- datasets::BOD
BOD
dataf(BOD, "Time", "demand")
BOD

On Wed, Aug 12, 2009 at 10:27 AM, Alexander Shenkin<ashenkin at ufl.edu> wrote:
> Hello All,
>
> I am trying to write a function which would operate on columns of a
> dataframe specified in parameters passed to that function.
>
>    f = function(dataf, col1 = "column1", col2 = "column2") {
>        dataf$col1 = dataf$col2 # just as an example
>    }
>
> The above, of course, does not work as intended.  In some languages one
> can force evaluation of a variable, and then use that evaluation as the
> variable name.  Thus,
>
>    > a = "myvar"
>    > (operator)a = 1
>    > myvar
>    [1] 1
>
> Is there some operator which allows this symbolic referencing in R?
>
> Thanks,
> Allie
>
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