Hi,

Is eval always used in conjunction with parse? Based on other languages, I'd expect the expression already to work without the use of parse(), but indeed it doesn't, or at least not as intended. Just a newbie question..

Cheers!!

Albert-Jan



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In the face of ambiguity, refuse the temptation to guess.

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--- On Sun, 3/21/10, jim holtman <jholtman@gmail.com> wrote:

From: jim holtman <jholtman@gmail.com>
Subject: Re: [R] using a condition given as string in subset function - how?
To: "Mark Heckmann" <mark.heckmann@gmx.de>
Cc: r-help@r-project.org
Date: Sunday, March 21, 2010, 2:33 AM

I know that if you have to resort to 'parse(text=...)', you should look for
another way (it is a 'fortune'), but it is getting late, and at least it
works:

> eval(parse(text="subset(df, A==1 & B==1)"))
  A B
1 1 1


On Sat, Mar 20, 2010 at 9:09 PM, Mark Heckmann <mark.heckmann@gmx.de> wrote:

> df <- data.frame(A=c(1,2), B=c(1,1))
>
> I have a string containing a condition for a subset function, like:
> conditionAsString <- paste(names(df), df[1,], sep="==", collapse=" & ")
>  > conditionAsString
>  > "A==1 & B==1"
>
> Now I want to use this string in the subset call, like
>
> subset(df, conditionAsString)
>
> I do not exactly now how to combine substitute, expression, parse and
> so on to get what I want, which would be:
>
> subset(df, A==1 & B==1)
>
> but using the string conditionAsString.
>
> Thanks,
> Mark
> –––––––––––––––––––––––––––––––––––––––
> Mark Heckmann
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
>
>
>
>
>
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>
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

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