[R] Turning strings into expressions

[Dimitris Rizopoulos]

Hi Alexander,

you could try:

my.string <- "A==1 & B==2"
(my.frame <- data.frame(A=sample(1:2, 20, TRUE), B=sample(1:2, 20, 
TRUE)))
subset(my.frame, eval(parse(text=my.string)))

I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Alexander Sokol" <alexandersokol at ofir.dk>
To: <r-help at stat.math.ethz.ch>
Sent: Thursday, November 25, 2004 2:09 PM
Subject: [R] Turning strings into expressions


> Hello,
>
> I am running R 1.9.1 om Windows 2000 SP4. My problem is as follows:
>
> Say I have a dataframe my.frame with column names A and B. I have a 
> string,
>
>>my.string
> [1] "A==1 & B==2"
>
> And I would like to retrieve the subset corresponding to my.string, 
> that is,
> from my.frame and my.string I would like to get the result of
>
> subset(my.frame,A==1 & B==2)
>
> So I need to find a way to convert
>
> "A==1 & B==2"
>
> to
>
> A==1 & B==2
>
> I at first hoped that get() could do the job, but this does not 
> work. Does
> anyone know how to do this?
>
> Thanks,
> Alexander
>
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