R help - Jun 2013 - Transforming boolean subsetting into index subsetting

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.

On Jun 28, 2013, at 23:58 , Julio Sergio 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.
> 
which(I)

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

?which

-- Bert

On Fri, Jun 28, 2013 at 2:58 PM, 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.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.


-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

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.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.