[R] Partial matching when using $ ? Feature or bug?

[Rainer M Krug]

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On 16/03/12 14:54, Sarah Goslee wrote:
> Hi Rainer,
> 
> On Fri, Mar 16, 2012 at 9:45 AM, Rainer M Krug <r.m.krug at gmail.com> wrote:
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>> 
>> Hi
>> 
>> I have the following code:
>> 
>> x <- data.frame(x1=1, x2=2, y1=3) x$y [1] 3 x$x NULL
> 
>> 
>> I was surprised (and definitely irritated?) when I realised that partial matching also works
>> for the $. Is this intended?
> 
> This is documented behavior, which by definition makes it a feature, right?

Not necessary - one can also document bugs. But I agree - this has to be considered a feature.

> 
> Both ‘[[’ and ‘$’ select a single element of the list.  The main difference is that ‘$’ does
> not allow computed indices, whereas ‘[[’ does.  ‘x$name’ is equivalent to ‘x[["name", exact = 
> FALSE]]’.  Also, the partial matching behavior of ‘[[’ can be controlled using the ‘exact’
> argument.
> 
> It's also a really good reason to use [[ in functions or anywhere there might be a chance of
> confusion.

Absolutely - I think I have to change my habit. I always prefered using $ as it seemed to me more
logical.

Thanks,

Rainer


> 
> Sarah
> 


- -- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys.
(Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

Tel :       +33 - (0)9 53 10 27 44
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email:      Rainer at krugs.de

Skype:      RMkrug
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