Executing a Function in a Loop With a ChangingValue foran Argument

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
PO Box 120, Cleveland, 4163
AUSTRALIA
Office Phone (email preferred): +61 7 3826 7251
Fax (if absolutely necessary):  +61 7 3826 7304
Mobile:                         +61 4 8819 4402
Home Phone:                     +61 7 3286 7700
mailto:Bill.Venables at csiro.au
http://www.cmis.csiro.au/bill.venables/ 

-----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
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.

______________________________________________
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.

Executing a Function in a Loop With a ChangingValue foran Argument

Thread (5 messages)