[R] the less-than-minus gotcha

[Greg Snow]

Steve (and any others still paying attention to this thread),

Larry Wall (author of Perl) said something along the lines of:

things that are similar should look similar, things that are different
should look different.

Ironically one of the first places I saw that quote was in a Perl vs.
Python language war and the same quote was being used by both sides.  This
made me think that you can learn a lot about how programmers think by what
they make look similar and what they make look different (and therefore
what they think are similar and different).

In R, I see the assignments:

foo( x <- something )

as assign to the variable x in the current (or calling) environment and

foo( x = something )

as assign to the variable x in the environment created by the function call.

With this distinction only "<-" makes any sense at the top level, but then
I see assigning to the 2 different environments as 2 different things that
should look different.  Using "=" for assignment makes sense if (and only
if) you consider assigning into different environments to be the same (or
at least very similar) thing.


Also you mentioned that

foo( x <- something )

should always be written as:

x <- something
foo(x)

and for many cases I agree, but consider the counter example of:

system.time( out <- longRunningSimulationFunction(n=1e6) )

compared to:

out = longRunningSimulationFunction(n=1e6)
system.time(out)

I would argue that the 1st version is much more useful than the 2nd.


On Mon, Feb 2, 2015 at 6:57 PM, Steve Taylor <steve.taylor at aut.ac.nz> wrote:

> Responding to several messages in this thread...
>
> > > All the more reason to use = instead of <-
> > Definitely not!
>
> Martin and Rolf are right, it's not a reason for that; I wrote that
> quickly without thinking it through.  An "=" user might be more likely to
> fall for the gotcha, if not spacing their code nicely.  So the lesson
> learned from the gotcha is that it's good to space your code nicely, as
> others have siad, not which assignment symbol to use.
>
> However, I continue to use "=" for assignment on a daily basis without any
> problems, as I have done for many years.  I remain unconvinced by any and
> all of these arguments against it in favour of "<-".  People telling me
> that I "should" use the arrow need better agruments than what I've seen so
> far.
>
> I find "<-" ugly and "->" useless/pointless, whereas "=" is simpler and
> also nicely familiar from my experience in other languages.  It doesn't
> matter to me that "=" is not commutative because I don't need it to be.
>
> > Further it can be nicely marked up by a real "left arrow"
> > by e.g. the listings LaTeX 'listings' package...
>
> Now that's just silly, turning R code into graphical characters that are
> not part of the R language.
>
> >  foo(x = y) and foo(x <- y)
>
> I'm well aware of this distinction and it never causes me any problems.
> The latter is an example of bad (obfuscated) coding, IMHO; it should be
> done in two lines for clarity as follows:
>
> x = y
> foo(x)
>
> > Using = has it's problems too.
> Same goes for apostrophes.
>
> Shall we discuss putting "else" at the start of line next?
>
> cheers,
>      Steve
>
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-- 
Gregory (Greg) L. Snow Ph.D.
538280 at gmail.com

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