DO NOT DO THIS!
This is a complete misuse of R.
R is not a macro/scripting language that constructs language expressions to
be evaluated (although it can do this). Rather, it is a functional language
that uses functions that build new objects from inputted objects and
parameters. I would strongly suggest reading An Introduction to R or other
R tutorial (there are many on the web) and perhaps relevant portions of the
R Language Definition manual to better understand what this means.You are
more or less wasting your time with R if you do not understand and use its
underlying programming paradigm.
The practical consequence of this dictum is that one should almost NEVER
use eval(parse()) -- instead construct a function that does what is needed.
In the present example, instead of doing what you and Arun have described,
do something like:
addthings <- function(x,y,a) {x + y + a} ## the curly brackets are
actually unnecessary
aa <- within(aa, z <- addthings(x,y,-2) )
-- Bert
On Wed, Sep 25, 2013 at 5:52 AM, arun <[email protected]> wrote:
> Also, Instead of ?attach, you could try ?with or ?within
> aa$z<- with(aa,eval(parse(text=bb)))
> aa$z
>
> #[1] 3 7 11
>
> aa<- within(aa,z<- eval(parse(text=bb)))
> aa
> # x y z
> #1 2 3 3
> #2 4 5 7
> #3 6 7 11
> A.K.
>
>
>
> ----- Original Message -----
> From: arun <[email protected]>
> To: R help <[email protected]>
> Cc:
> Sent: Wednesday, September 25, 2013 8:47 AM
> Subject: Re: Re: Creating a new column to a data frame using a formula
> from another variable
>
> Hi,
>
> Change:
> aa$z<- eval(parse(text=bb))
>
> aa
> # x y z
> #1 2 3 3
> #2 4 5 7
> #3 6 7 11
> A.K.
>
> I want to create a new column to a data frame using a formula from another
> variable:
> Example:
> I have a data set "aa" is;
> x y
> 2 3
> 4 5
> 6 7
>
> My R code is;
> >bb <- "x+y-2"
> >attach(aa)
> >aa$z<- bb
> >detach(aa)
>
> the result is;
> x y z
> 2 3 x+y-2
> 4 5 x+y-2
> 6 7 x+y-2
>
> but I want like;
> x y z
> 2 3 3
> 4 5 7
> 6 7 11
>
> Could you please help me..
>
> ______________________________________________
> [email protected] 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.
>
--
Bert Gunter
Genentech Nonclinical Biostatistics
Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
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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.
