[R] transform() on selective names. Is it possible?

[David Winsemius]

On Apr 7, 2011, at 10:27 AM, Juan Carlos Borrás wrote:

> 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.

I haven't stumbled on a solution to that task. I am wondering if you  
could use something like:

inpnames <- names(dfrm) # before the transform step
outdfrm <- transform(...)
names(outdfrm) <- c(inpnames, paste(colxy, "new", sep="_") )

.... kludgy to be sure.

> 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 Borrás 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!
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
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>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> David Winsemius, MD
>> West Hartford, CT
>>
>>
>
>
> Cheers,
> jcb!

David Winsemius, MD
West Hartford, CT