The explanation seems to be in different behaviour of the
substitute(...) construction:
R:> f<-function(a,b){a<-1; print(deparse(substitute(c(a,b))))}
> f(a,b)
[1] "c(1, b)"
Splus:> f<-function(a,b){a<-1; print(deparse(substitute(c(a,b))))}
> f(a,b)
[1] "c(a, b)"
[1] "c(a, b)"
So in R, assignment to a formal parameter causes the changed value to
be used for substitution purposes.
In S, this does not happen *unless the formal parameter is a
constant.*!
> f(2,b)
[1] "c(1, b)"
[1] "c(1, b)"> f(2:2,b)
[1] "c(2:2, b)"
[1] "c(2:2, b)"> f("a",b)
[1] "c(1, b)"
[1] "c(1, b)"
This is confusing in both languages, but I'd say that S has the bigger
problem...
In Kurts example, inserting
xlab
ylab
as the first two lines of the function defeats lazy evaluation and
provides the desired behaviour (I suppose) in both R and S.
- Peter
----
Kurt Hornik <Kurt.Hornik@ci.tuwien.ac.at> writes:
> "test" <-
> function(x, y, xlab = deparse(substitute(x)), ylab =
deparse(substitute(y)))
> {
> x <- sort(x)
> print(xlab)
> n <- length(x)
> y <- (1:n) / n
> print(ylab)
> }
>
> Under R,
>
> R> test(4:1)
> [1] "c(1, 2, 3, 4)"
> [1] "c(0.25, 0.5, 0.75, 1)"
> R> test(4:1, 4)
> [1] "c(1, 2, 3, 4)"
> [1] "c(0.25, 0.5, 0.75, 1)"
>
> Under S,
>
> > test(4:1)
> [1] "4:1"
> [1] ""
> [1] ""
> > test(4:1, 4)
> [1] "4:1"
> [1] "c(0.25, 0.5, 0.75, 1)"
> [1] "c(0.25, 0.5, 0.75, 1)"
>
> ???
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907
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