advice/opinion on "<-" vs "=" in teaching R

On Fri, Jan 15, 2010 at 2:38 PM, Ted Harding
<Ted.Harding at manchester.ac.uk> wrote:

On 15-Jan-10 08:14:04, Barry Rowlingson wrote:

On Fri, Jan 15, 2010 at 6:57 AM, Ted Harding
<Ted.Harding at 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?

?_Remember: 'eschew obfuscation'.

Barry

Tasteless or not, the language allows it to be done; and therefore
discussion of distinctions between ways of doing it is relevant to
Erin's question!

While I am at it, in addition to the above example, we can have

?_x <- 1.234
?_sqrt(x=4)
?_# [1] 2
?_x
?_# [1] 1.234

compared with (as in the first example):

?_x <- 1.234
?_sqrt(x<-4)
?_# [1] 2
?_x
?_# [1] 4

There is a passage in ?"<-" (which I don't completely understand)
which is also relevant to Erin's query about '=' vs '<-':

?_The operators '<-' and '=' assign into the environment in
?_which they are evaluated. ?_The operator '<-' can be used
?_anywhere, whereas the operator '=' is only allowed at the
?_top level (e.g., in the complete expression typed at the
?_command prompt) or as one of the subexpressions in a braced
?_list of expressions.

(I'm not too clear about the scope of "one of the subexpressions
in a braced list of expressions").

For example:

x = xyplot(1~1)
system.time(x = xyplot(1~1))

Error in system.time(x = xyplot(1 ~ 1)) :
  unused argument(s) (x = xyplot(1 ~ 1))

system.time({ x = xyplot(1~1) })

   user  system elapsed
  0.008   0.000   0.005

Of course, <- would not have had a problem. This is the most common
problem I personally have had using = for assignment (better
readability of <- is also a huge plus).

-Deepayan