[R] convert text to exprission good for lm arguments

[Gabor Grothendieck]

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
>
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