[R] evaluate one variable in an expression with two variables

[Gabor Grothendieck]

On Wed, Feb 8, 2012 at 4:02 PM, moli <nirdong at gmail.com> wrote:
> I want to evaluate f with the mean=7
>
>  mean=7
>  f <-  expression(-(x-mean)^2/2)
> then get a new expression:
>
>  -(x-7)^2/2
> How could I do it? Thanks.
>

You can leave out the initial as.expression if you don't mind having a
call object instead:

> as.expression(do.call("substitute", list(f[[1]], list(mean = 7))))
expression(-(x - 7)^2/2)

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