R help - Jul 2006 - Splitting the left and right hand terms of a formula

Let's say I have the following formula:

a.formula <- x ~ y + z

I want to extract the left and right-hand sides of the function so
that I have two character vectors like the ones you would create using
the following assignments:

left.hand.side <- "x"
right.hand.side <- c("y", "z")

One way to do this follows:

left.hand.side <- unlist(dimnames(attr(terms(a.formula),
"factors"))[1])
right.hand.side <- unlist(dimnames(attr(terms(a.formula),
"factors"))[-1])

Is there a better or cleaner way to do this?

Thanks!

Daniel Gerlanc
Williams College '07

Try this:
> all.vars(update(a.formula, .~0))
[1] "x"
> all.vars(update(a.formula, 0~.))
[1] "y" "z"

On 7/14/06, Daniel Gerlanc <dgerlanc at gmail.com>
wrote:
> Let's say I have the following formula:
>
> a.formula <- x ~ y + z
>
> I want to extract the left and right-hand sides of the function so
> that I have two character vectors like the ones you would create using
> the following assignments:
>
> left.hand.side <- "x"
> right.hand.side <- c("y", "z")
>
> One way to do this follows:
>
> left.hand.side <- unlist(dimnames(attr(terms(a.formula),
"factors"))[1])
> right.hand.side <- unlist(dimnames(attr(terms(a.formula),
"factors"))[-1])
>
> Is there a better or cleaner way to do this?
>
> Thanks!
>
> Daniel Gerlanc
> Williams College '07
>
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