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 <smartpink111@yahoo.com> 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 <smartpink111@yahoo.com>
> To: R help <r-help@r-project.org>
> 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..
>
> ______________________________________________
> R-help@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.
>



-- 

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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