[R] Executing a Function in a Loop With a ChangingValue foran Argument
Bill.Venables at csiro.au
Bill.Venables at csiro.au
Thu Oct 25 08:26:22 CEST 2007
I wondered if the real problem was bigger than your abstract version.
OK. Here is one way to do it
> myfunc <- function(x) {
nam <- deparse(substitute(x))
val <- mean(x)
cat("mean(", nam, ") =", val, "\n")
invisible(val)
}
> ex <- quote(myfunc(x))
> subst <- function(Command, ...) do.call("substitute", list(Command,
list(...)))
> dat <- data.frame(matrix(rnorm(25), 5, 5))
> vars <- names(dat)[-1]
> vars
[1] "X2" "X3" "X4" "X5"
> for(i in vars) with(dat, eval(subst(ex, x = as.symbol(i))))
mean( X2 ) = -0.08661249
mean( X3 ) = 0.009840606
mean( X4 ) = -0.21054
mean( X5 ) = 0.07321301
> colMeans(dat[, -1])
X2 X3 X4 X5
-0.086612490 0.009840606 -0.210540008 0.073213012
>
Now why do I suspect there is something more as well....hmmm...?
Bill Venables
CSIRO Laboratories
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mailto:Bill.Venables at csiro.au
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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Rick Bilonick
Sent: Thursday, 25 October 2007 4:13 PM
To: R Help
Subject: Re: [R] Executing a Function in a Loop With a ChangingValue
foran Argument
On Thu, 2007-10-25 at 15:34 +1000, Bill.Venables at csiro.au wrote:
> There are many simple ways to do this, if I understand you correctly.
> Here is an example
>
> > dat <- data.frame(matrix(rnorm(25), 5, 5))
> > names(dat)
> [1] "X1" "X2" "X3" "X4" "X5"
> > vars <- names(dat)[-1]
> > vars
> [1] "X2" "X3" "X4" "X5"
> > myfunc <- function(x) print(mean(x))
> > for(i in dat[, vars]) myfunc(x = i)
> [1] 0.3648022
> [1] -0.1593466
> [1] 0.5874517
> [1] -0.5049586
> > colMeans(dat) ## as a check
> X1 X2 X3 X4 X5
> 0.1779146 0.3648022 -0.1593466 0.5874517 -0.5049586
> >
>
>
> Bill Venables
>
Thanks. The problem with this approach is that the data.frame variable
names are lost. (A minor point is that it won't work if only one
variable is chosen.) The function I wrote generates labels for a plot
and I want the variable name to show up (not "i"). I was hoping not to
have to re-write my function. Is there a way to pass the variables that
will allow my function to work normally (just as it would if I wrote out
the function calls with the names manually inserted)? (I would assume
that any function that generates a character variable from the variable
name is not going to produce the desired result.)
Rick B.
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