[R] evaluation of expressions

[Gabor Grothendieck]

Try this:

e <- expression(glm(y ~ age))
eval(e)

or this:

chr <- "glm(y ~ age)"
eval(parse(text = chr))

On 5/2/06, Andrew Gelman <gelman at stat.columbia.edu> wrote:
> Hi, all.  I'm trying to automate some regression operations in R but am
> confused about how to evaluate expressoins that are expressed as
> character strings.  For example:
>
> y <- ifelse (rnorm(10)>0, 1, 0)
> sex <- rnorm(10)
> age <- rnorm(10)
> test <- as.data.frame (cbind (y, sex, age))
>
> # this works fine:
> glm (y ~ sex + I(age^2), data=test, family=binomial(link="logit"),
> subset=age<1)
>
> # but now I want to do it in two steps:
> expr <- 'glm (y ~ sex + I(age^2), data=test,
> family=binomial(link="logit"), subset=age<1)'
>
> Given "expr", defined above, how can I evaluate it?  I played around
> with eval() and as.expression() but can't figure it out.
>
> Thanks.
> Andrew
>
> --
> Andrew Gelman
> Professor, Department of Statistics
> Professor, Department of Political Science
> gelman at stat.columbia.edu
> www.stat.columbia.edu/~gelman
>
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