On 01/10/2019 4:58 a.m., Serguei Sokol wrote:
Le 30/09/2019 à 16:17, Duncan Murdoch a écrit :
There's a StackOverflow question
https://stackoverflow.com/q/22024082/2554330 that references this text
from ?missing:
"Currently missing can only be used in the immediate body of the
function that defines the argument, not in the body of a nested
function or a local call. This may change in the future."
Someone pointed out (in https://stackoverflow.com/a/58169498/2554330)
that this isn't true in the examples they've tried: missingness does
get passed along. This example shows it (this is slightly different
than the SO example):
f1 <- function(x, y, z){
if(missing(x))
cat("f1: x is missing\n")
if(missing(y))
cat("f1: y is missing\n")
}
f2 <- function(x, y, z){
if(missing(z))
cat("f2: z is missing\n")
f1(x, y)
}
f2()
which produces
f2: z is missing
f1: x is missing
f1: y is missing
Is the documentation out of date? That quote appears to have been
written in 2002.
Er, as far as I understand the cited doc, it correctly describes what
happened in your example: missing() is not working in a local call (here
f1(x,y)).
In fact, what missing() of f1 is reporting it is still the situation of
f2() call (i.e. immediate body of the function). See
f2(y=1)
produces
f2: z is missing
f1: x is missing
(the line about y missing disappeared from f1(x,y) call, what needed to
be demonstrated).
Yes, that's a possible interpretation. Another one is that missing
should fail in this example:
f2 <- function(z){
f1 <- function(){
if(missing(z))
cat("f1: z is missing\n")
}
f1()
}
and it does:
> f2()
Error in missing(z) (from #3) : 'missing' can only be used for arguments
Here missing() is appearing in a nested function. I'm really not sure
which is the intended meaning of that paragraph: what exactly is a
"local call"?
Duncan Murdoch
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