> On 14 Aug 2016, at 11:23 , Luca Cerone <luca.cer...@gmail.com> wrote:
>
> I have no access to my laptop so I can't double check but I think in one of
> Wickham's book there was an example like
>
> f <- function (y) {
> substitute (x + y)
> }
>
> f(4)
> [1] x + 4
>
> i.e. where substitute inside a function was substituting the value of y and
> returned the expression replacing y with 4, which is what I would expect to
> happen.
>
In a word: no.
> f <- function (y) {
+ substitute (x + y)
+ }
>
> f(4)
x + 4
> f(z)
x + z
i.e., it is not the value of y, but the expression passed for y that gets
substituted.
There are subtleties: If y is computed inside the function, the connection to
the argument expression is lost, and then the value is in fact used:
> z <- pi
> f <- function (y) { y <- y
+ substitute (x + y)
+ }
> f(z)
x + 3.14159265358979
It is usually a better idea to handle these issues with bquote(), though.
--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd....@cbs.dk Priv: pda...@gmail.com
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