R help - May 2007 - convert text to exprission good for lm arguments

Hi, 

I ran into a problem of converting a text representation of an expression into
parsed expression to be further evaluated inside lm ().
> n <- 100 
> data <- data.frame(x= rnorm (n), y= rnorm (n)) 
> data. lm <- lm (y ~ x, data=data) 
> 
> ## this works 
> update(data. lm , subset=x<0) 
Call: 
lm (formula = y ~ x, data = data, subset = x < 0) 

Coefficients: 
(Intercept) x 
-0.07864094193322170023 -0.14596982635007796358 
> 
> ## this doesn't work 
> ## text representation of subset 
> subset <- "x<0" 
> update(data. lm , subset=parse(text=subset)) 
Error in `[.data.frame`(list(y = c(-0.601925958140825, -0.111931189071517, : 
invalid subscript type 

What is the correct way to convert "x<0" into a valid subset
argument?

Thanks, 
Vadim 

	[[alternative HTML version deleted]]

Try:

do.call("update", list(data.lm, subset = parse(text = subset)))

On 5/3/07, Vadim Ogranovich <vogranovich at jumptrading.com>
wrote:
> Hi,
>
> I ran into a problem of converting a text representation of an expression
into parsed expression to be further evaluated inside lm ().
>
> > n <- 100
> > data <- data.frame(x= rnorm (n), y= rnorm (n))
> > data. lm <- lm (y ~ x, data=data)
> >
> > ## this works
> > update(data. lm , subset=x<0)
>
> Call:
> lm (formula = y ~ x, data = data, subset = x < 0)
>
> Coefficients:
> (Intercept) x
> -0.07864094193322170023 -0.14596982635007796358
>
> >
> > ## this doesn't work
> > ## text representation of subset
> > subset <- "x<0"
> > update(data. lm , subset=parse(text=subset))
> Error in `[.data.frame`(list(y = c(-0.601925958140825, -0.111931189071517,
:
> invalid subscript type
>
> What is the correct way to convert "x<0" into a valid subset
argument?
>
> Thanks,
> Vadim
>
>        [[alternative HTML version deleted]]
>
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>

Vadim Ogranovich wrote:
> 
> Hi, 
> 
> I ran into a problem of converting a text representation of an expression
> into parsed expression to be further evaluated inside lm (). 
> 
>> n <- 100 
>> data <- data.frame(x= rnorm (n), y= rnorm (n)) 
>> data. lm <- lm (y ~ x, data=data) 
>> 
>> ## this works 
>> update(data. lm , subset=x<0) 
> 
> Call: 
> lm (formula = y ~ x, data = data, subset = x < 0) 
> 
> Coefficients: 
> (Intercept) x 
> -0.07864094193322170023 -0.14596982635007796358 
> 
>> 
>> ## this doesn't work 
>> ## text representation of subset 
>> subset <- "x<0" 
>> update(data. lm , subset=parse(text=subset)) 
> Error in `[.data.frame`(list(y = c(-0.601925958140825, -0.111931189071517,
> : 
> invalid subscript type 
> 
> What is the correct way to convert "x<0" into a valid subset
argument?
> 
update(data.lm,subset=eval(parse(text=subset)))
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