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

From: Juan Carlos Borrás <jcborras_at_gmail.com>
Date: Thu, 07 Apr 2011 17:27:39 +0300

# 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")

fc <- function(dfrm, coln) transform(dfrm, coln=whiten(dfrm[,coln])) colxy <- "x"
z2 <- fc(z, colxy) # the "[" function will interpret colxy colnames(z2)
>  "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 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)
>>>
>>>  "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")
>>
>>>
>>>        x         y
>>> 1 17.167380  6.884402
>>> 2  8.234507 13.940932
>>
>>>
>>>        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?
>> jcb!
>>
>> ______________________________________________
>> R-help_at_r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>
>

Cheers,
jcb!

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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. Received on Thu 07 Apr 2011 - 14:33:03 GMT

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