[R] unique deletes names - intended?

[Prof Brian Ripley]

On Tue, 4 Jul 2006, Heinz Tuechler wrote:

> Dear All,
>
> as shown in the example, unique() deletes names of vector elements.
> Is this intended?

Yes.  Think of the vector as a set: it is supposed to immaterial which of 
the duplicated elements is retained.

The help page says

      An object of the same type of 'x'. but if an element is equal to
      one with a smaller index, it is removed.

so it is starting with a new object, not 'x'.  However, the array method 
works differently, so the documentation needs clarification.

> Of course, one can use indexing by !duplicated() instead.

Be careful, as you might get a method for [ and that might not do want you 
intended (e.g. for a time series).


> Greetings,
> Heinz
>
> ## unique deletes names
> v1 <- c(a=1, b=2, c=3, e=2, a=4)
> unique(v1) # names deleted
>
> v1[!duplicated(v1)] # names preserved
>
>
> platform       i386-pc-mingw32
> arch           i386
> os             mingw32
> system         i386, mingw32
> status         Patched
> major          2
> minor          3.1
> year           2006
> month          07
> day            01
> svn rev        38471
> language       R
> version.string Version 2.3.1 Patched (2006-07-01 r38471)
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595