[R] Turning a logical vector into its indices without losing its length

[Gabor Grothendieck]

Here are two solutions:

> logvec <- c(TRUE,FALSE,FALSE,TRUE,FALSE,FALSE,TRUE,FALSE)

> ifelse(logvec, seq_along(logvec), 0)
[1] 1 0 0 4 0 0 7 0

> replace(logvec * 0, logvec, which(logvec))
[1] 1 0 0 4 0 0 7 0


On 8/24/07, Leeds, Mark (IED) <Mark.Leeds at morganstanley.com> wrote:
> I have the code below which gives me what I want for temp based on
> logvec but I was wondering if there was a shorter way ( i.e :
> a one liner ) without having to initialize temp to zeros.  This is
> purely for learning purposes. Thanks.
>
> logvec <- c(TRUE,FALSE,FALSE,TRUE,FALSE,FALSE,TRUE,FALSE)
>
> temp<-numeric(length(invec))
> temp[invec]<-which(invec)
> temp
>
> [1] 1 0 0 4 0 0 7 0
>
> obviously, the code below doesn't work.
>
> temp <- which(invec)
> > temp
> [1] 1 4 7
> --------------------------------------------------------
>
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