R help - Jul 2009 - subsetting a dataframe with a string logical expression

Hi,

I am trying to subset a dataset based on a filter defined by a user... 
I prompt the user for input.. resulting in a string logical expression 
("X1 < 3").

I have tried using subset, but it is looking for a logical expression, not 
a character string.
I keep getting the error:  'subset' must evaluate to logical.


Example:
x <- data.frame(matrix(1:15, nrow=5, ncol=3))
filter = "X1 < 3"
subset(x, filter)


Any ideas??



Thanks much,
Tracey

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Try this:

subset(x, eval(parse(text=filter)))


On Wed, Jul 8, 2009 at 4:46 PM, Tracey Frescino <tfrescino@fs.fed.us>
wrote:
> Hi,
>
> I am trying to subset a dataset based on a filter defined by a user...
> I prompt the user for input.. resulting in a string logical expression
> ("X1 < 3").
>
> I have tried using subset, but it is looking for a logical expression, not
> a character string.
> I keep getting the error:  'subset' must evaluate to logical.
>
>
> Example:
> x <- data.frame(matrix(1:15, nrow=5, ncol=3))
> filter = "X1 < 3"
> subset(x, filter)
>
>
> Any ideas??
>
>
>
> Thanks much,
> Tracey
>
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>
> ______________________________________________
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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.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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