Barry Rowlingson wrote:
On Fri, Jan 15, 2010 at 6:57 AM, Ted Harding
<ted.hard...@manchester.ac.uk>wrote:
There is at least one context where the distinction must be
preserved. Example:
pnorm(1.5)
# [1] 0.9331928
pnorm(x=1.5)
# Error in pnorm(x = 1.5) : unused argument(s) (x = 1.5)
pnorm(x<-1.5)
# [1] 0.9331928
x
# [1] 1.5
Ted.
I would regard modifying a variable within the parameters of a function
call as pretty tasteless. What does:
foo(x<-2,x)
or
foo(x,x<-3)
do that couldn't be done clearer with two lines of code?
The most common use I see that I like is within a conditional test like
if ( !is.null(x <- get("x", somehow)) && length(x) == 1) { dosomething }
The x variable is only used for the test, but since it is used twice
there, the assignment saves getting it twice. You could expand it to
two lines
x <- get("x", somehow)
if ( !is.null(x) && length(x) == 1) { dosomething }
but I find that a tiny bit harder to read.
On the other hand, I would never use the examples you gave, because I'd
have no idea what the value of x would be, since it depends on the order
of evaluation of the arguments. In R, I don't even know for sure if the
assignment would be evaluated at all, let alone before the x argument.
Duncan Murdoch
Remember: 'eschew obfuscation'.
Barry
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
