[R] Transforming boolean subsetting into index subsetting

[Jim Holtman]

which ( abs(V - 9) <= 3 )

Sent from my iPad

On Jun 28, 2013, at 17:58, Julio Sergio <juliosergio at gmail.com> wrote:

> One of the techniques to subset, a vector for instance, is the following:
> 
>  V <- c(18, 8, 5, 41, 8, 7)
>  V
>  ## [1] 18  8  5 41  8  7
>  ( I <- abs(V - 9) <= 3 )
>  ## [1] FALSE  TRUE FALSE FALSE  TRUE  TRUE
>  V[I]
>  ## [1] 8 8 7
> 
> However, sometimes we are interested in the indexes of the elements where the 
> condition holds. Is there an easy way to transform the I vector into an 
> indexes vector similar to:  I == c(2,5,6) ?
> 
> I know that I can traverse the I vector with a for() loop collecting the 
> indexes, I just wonder if such an operation can be avoided.
> 
> Thanks,
> 
>  -Sergio.
> 
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