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

[Prof Brian Ripley]

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/
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