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

[(Ted Harding)]

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").

Ted.

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Date: 15-Jan-10                                       Time: 09:08:41
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