[R] Strange case of partial matching in .[ - possible bug / wrong documentation?

Hilmar Berger hilmar.berger at integromics.com
Wed May 19 22:41:18 CEST 2010

Duncan Murdoch schrieb:
> On 19/05/2010 12:14 PM, Hilmar Berger wrote:
>> Hi all,
>> This occurred in R-2.11.0 (WinXP).
>> The R-help page of .[ says that:
>> "Character indices can in some circumstances be partially matched (see
>> pmatch) to the names or dimnames of the object being subsetted (but 
>> never
>> for subassignment). Unlike S (Becker et al p. 358)), R has never used
>> partial matching when extracting by [, and as from R 2.7.0 partial 
>> matching
>> is not by default used by [[ (see argument exact)."
>> My understanding is therefore that .[ should never try partial matching.
> See near the top of the page:  "The descriptions here apply only to 
> the default methods."  Since indexing is generic, an extraction method 
> can do whatever it wants, and you need to read the particular page to 
> find the behaviour.  The page for Extract.data.frame says:
> "Both |[| and |[[| extraction methods partially match row names. By 
> default neither partially match column names, but |[[| will unless 
> |exact=TRUE|. If you want to do exact matching on row names use |match 
> <>| as in the examples."
> Duncan Murdoch 
Sorry, I should have read the complete help page.

Thanks a lot !

Best regards,

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