[R] difference between assignment syntax <- vs =

Thomas Lumley tlumley at u.washington.edu
Mon Feb 23 11:51:02 CET 2009


On Mon, 23 Feb 2009, Patrick Burns wrote:

> Since this topic came up, I've been thinking that
> that sentence needs more work.
>
> The "standard" is not from me -- I'm a bit more
> agnostic than the statement although I personally
> always use '<-'.  I'm thinking a revised version
> might be something along the lines of:
>
> Standard advice from most long-time R users is
> to avoid using '=' when you mean '<-'.  However,
> as long as you avoid the traps, it is really a matter
> of taste.

Although it's probably true that most long-time R users use <-, this is at least in part because a long-time R user would initially have had to use <-, since = wasn't available in the distant past.

I would say that it's entirely a matter of taste -- the things that otherwise could have been traps are mostly syntax errors.  The only proviso is that if you post code using = it is (even more) important to leave spaces around the = than it would be for <-.

      -thomas


> Rejoinders, etc. will be considered for whenever
> a revised Inferno appears.
>
> Pat
>
>
> Thomas Mang wrote:
>> Hi,
>> 
>> thanks for the link.
>> 
>> In the bottom part of the relevant section, you say:
>> "Standard advice is to avoid using '=' when you mean '<-'...."
>> Is this a formal, generally accepted (R community) advice, or does it 
>> reflect you personal opinion?
>> Note I am not asking this question as to criticize by any means, but instead 
>> I just want to know for my own work (which will be partially released to 
>> others) if the '<-' - style is the preferred one (Personally, with a strong 
>> background from other programming languages, I have always used '=' so far).
>> 
>> thanks,
>> Thomas
>> 
>> 
>> 
>> Patrick Burns wrote:
>>> 'The R Inferno' page 78 is one source you can
>>> look at.
>>> 
>>> 
>>> Patrick Burns
>>> patrick at burns-stat.com
>>> +44 (0)20 8525 0696
>>> http://www.burns-stat.com
>>> (home of "The R Inferno" and "A Guide for the Unwilling S User")
>>> 
>>> Thomas Mang wrote:
>>>> Hi,
>>>> 
>>>> Both operators <- and = can be used to make an assignment. My question 
>>>> is: Is there a semantic difference between these two? Some time ago, I 
>>>> remember I have read that because of some reason, one should be given 
>>>> preference over the other - but I cannot remember the source, nor the 
>>>> argument, nor which operator the preferred was.
>>>> 
>>>> What is the present state ?
>>>> Is still one version better than the other, or is it only a matter of 
>>>> taste what to use ?
>>>> 
>>>> thanks
>>>> Thomas
>>>> 
>>>> ______________________________________________
>>>> R-help at 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.
>>>> 
>>>> 
>>> 
>>> ______________________________________________
>>> R-help at 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.
>>> 
>> 
>> ______________________________________________
>> R-help at 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.
>> 
>> 
>
> ______________________________________________
> R-help at 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.
>

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle



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