R help - Apr 2008 - What to use for assignment, " = " or " <- "?

I've noticed an increasing tendency for people to use '=' rather
than
the older '<-' symbol.  When '=' became available as an
assignment
operator in S-PLUS in the late '90s my first reaction was to switch to
it as well.  Brian Ripley warned me that it was not a good idea.  As
usual he was right, but it took a couple of pretty serious
finger-burning episodes before I came fully around to his view.

There are three left assignment operators in S, and it's a good idea to
distinguish what they do.

a <<- b
	assigns a value 'b' to an object 'a' in some parent environment

a <- b
	assigns a value 'b' to an object 'a' in the current environment

a = b (inside the argument list of a function call)
	potentially assigns a value 'b' to an object 'a' in the child
environment of the function.  Lazy evaluation determines if it actually
happens or not.

You must use '=' for the third of these.  If you choose to use it for
the second as well, as is allowed, there is a danger that you will
confuse the environment in which the assignment is actually made.  It's
not a great danger, of course, but it can happen.  In any case, it is a
good idea to use three separate operators for these three distinct
purposes, if nothing else as a clear visual reminder of what kind of
assignment is intended to take place.

I suspect the push towards using '=' instead of '<-' has two
main
drivers:

1. the world is full of lazy typists

2. right now there seems to be a big influx of Matlab people into R, and
it makes them feel more at home.

Neither of these is much of a reason, I reckon.

Bill Venables
CSIRO Laboratories
PO Box 120, Cleveland, 4163
AUSTRALIA
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http://www.cmis.csiro.au/bill.venables/

<Bill.Venables <at> csiro.au> writes:
> 
> I've noticed an increasing tendency for people to use '='
rather than
> the older '<-' symbol.  When '=' became available as an
assignment
> operator in S-PLUS in the late '90s my first reaction was to switch to
> it as well.  Brian Ripley warned me that it was not a good idea.  As
> usual he was right, but it took a couple of pretty serious
> finger-burning episodes before I came fully around to his view.
> 
  [snip]
> I suspect the push towards using '=' instead of '<-' has
two main
> drivers:
> 
> 1. the world is full of lazy typists
> 
> 2. right now there seems to be a big influx of Matlab people into R, and
> it makes them feel more at home.
> 
> Neither of these is much of a reason, I reckon.
> 
  
   It may not be a good reason, but the reason I usually
teach "=" rather than "<-" to my students is that they
are
usually learning scripting/programming for the very first
time, and the "=" syntax for assignment (which as I recall
was called "gozzinta", for "goes into", in the FORTRAN
coloring
book) seems natural to most people (even though it's 
logically quite different).  They are so overwhelmed by
learning new things that I don't want to add one more.
(This is admittedly a judgment call.)

  Ben Bolker