Re: [R] selecting values that are unique, instead of selecting unique values

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Wed, 25 Jun 2008 17:43:30 +0100 (BST)

On Wed, 25 Jun 2008, Marc Schwartz wrote:

> on 06/25/2008 11:19 AM Daren Tan wrote:
>>
>> unique(c(1:10,1)) gives 1:10 (i.e. unique values), is there any
>> method to get only 2:10 (i.e. values that are unique) ?
>>
>
> The easiest might be:
>
>> Vec
> [1] 1 2 3 4 5 6 7 8 9 10 1
>
>> Vec[table(Vec) == 1]
> [1] 2 3 4 5 6 7 8 9 10

I don't think that is right: you are relying on recycling indices. Try

Vec <- c(1,1:10)
Vec[table(Vec) == 1]

which should be the same.

I was about to write

tab <- table(Vec)
names(tab)[tab==1]

but that gives a character vector. Here's a different way:

Vec[rowSums(outer(Vec, Vec, "=="))==1]

-- 
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

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Received on Wed 25 Jun 2008 - 16:46:58 GMT

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