transform() on selective names. Is it possible?

Wonderful, or the closest to heaven I've been the whole afternoon, but
not quite there:

# begin code
N <- 300
M <- 2
x <- matrix(data=rnorm(N*M, 0, 3)-10, ncol=M, nrow=N)
y <- matrix(c(1,-2,-2,1), ncol=M, nrow=M)
z <- data.frame(x %*% y)
colnames(z) <- c('x','y')
par(mfrow=c(1,3))
plot(z, pch=5, col="blue")

whiten <- scale  # no need to re-invent the wheel, I agree
fc <- function(dfrm, coln) transform(dfrm, coln=whiten(dfrm[coln]))
colxy <- "x"
z1 <- fc(z, colxy)  # the "[" function will interpret colxy
colnames(z1)

[1] "x"   "y"   "x.1"

fc <- function(dfrm, coln) transform(dfrm, coln=whiten(dfrm[,coln]))
colxy <- "x"
z2 <- fc(z, colxy)  # the "[" function will interpret colxy
colnames(z2)

[1] "x"    "y"    "coln"

#end code

What I want is to know whether I can customize the column name of the
result of the transform() call.

Your hint is fantastic, thanks there, but I keep getting into that
particular pattern of computation over and over and I wonder if it's
possible to skip a column clean-up after applying your trick.

2011/4/7 David Winsemius <dwinsemius at comcast.net>:

On Apr 7, 2011, at 9:56 AM, Juan Carlos Borr?s wrote:

Hi all,
I am whitening my data:

# code begins
N <- 300
M <- 2
x <- matrix(data=rnorm(N*M, 0, 3)-10, ncol=M, nrow=N)
y <- matrix(c(1,-2,-2,1), ncol=M, nrow=M)
z <- data.frame(x %*% y)
colnames(z) <- c('x','y')
par(mfrow=c(1,3))
plot(z, pch=5, col="blue")

whiten <- function(x) { (x-mean(x))/sd(x) }

Consider:

 whiten <- scale  # no need to re-invent the wheel
 fc <- function(dfrm, coln) transform(dfrm, coln=whiten(dfrm[coln]))
 colxy <- "x"
 z <- fc(z, colxy)  # the "[" function will interpret colxy
 z

zz <- transform(z, x=whiten(x), y=whiten(y))
plot(zz, pch=3, col="red")

#code ends

And everything looks fine enough.
But now I want to withen just one of the columns and I won't know
which one until my script is running, hence I can't hard code it in
the script.
Then I though, well maybe if I define some convenient f...

#begin code

f <- function(a) { paste(a,"=withen(",a,")", sep='') }
a <- 'x' # or a <- 'y' depending on user input.....
f(a)

[1] "x=withen(x)"

# so I could try....
zzz <- transform(z, eval(f('x')))
# which of course doesn't work
plot(zz, pch=3, col="green")

head(z, n=2)

       x         y
1 17.167380  6.884402
2  8.234507 13.940932

head(zzz, n=2)

       x         y
1 17.167380  6.884402
2  8.234507 13.940932

#end code

Could someone provide me with some hint on whether the attempted  
trick
above is possible and how to proceed further?
Thanks in advance.
jcb!

David Winsemius, MD
West Hartford, CT

Cheers,
jcb!