From: Ray Brownrigg <ray_at_mcs.vuw.ac.nz>

Date: Wed 25 Jan 2006 - 08:32:32 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Jan 25 10:40:23 2006

Date: Wed 25 Jan 2006 - 08:32:32 EST

There's an even faster one, which nobody seems to have mentioned yet:

rep(l <- rle(ids)$lengths, l)

Timing on my 2.8GHz NetBSD system shows:

> length(ids)

[1] 45150

> # Gabor:

> system.time(for (i in 1:100) ave(as.numeric(factor(ids)), ids, FUN =

length))

[1] 3.45 0.06 3.54 0.00 0.00

> # Barry (and others I think):

> system.time(for (i in 1:100) table(ids)[ids])

[1] 2.13 0.05 2.20 0.00 0.00

*> Me:
*

> system.time(for (i in 1:100) rep(l <- rle(ids)$lengths, l))

[1] 1.60 0.00 1.62 0.00 0.00

Of course the difference between 21 milliseconds and 16 milliseconds is not great, unless you are doing this a lot.

Ray Brownrigg

*> From: Gabor Grothendieck <ggrothendieck@gmail.com>
**>
*

> Nice. I timed it and its much faster than mine too.

*>
**> On 1/24/06, Barry Rowlingson <B.Rowlingson@lancaster.ac.uk> wrote:
**> > Laetitia Marisa wrote:
**> > > Hello,
**> > >
**> > > Is there a simple and fast function that returns a vector of the number
**> > > of replications for each object of a vector ?
**> > > For example :
**> > > I have a vector of IDs :
**> > > ids <- c( "ID1", "ID2", "ID2", "ID3", "ID3","ID3", "ID5")
**> > >
**> > > I want the function returns the following vector where each term is the
**> > > number of replicates for the given id :
**> > > c( 1, 2, 2, 3,3,3,1 )
**> >
**> > One-liner:
**> >
**> > > table(ids)[ids]
**> > ids
**> > ID1 ID2 ID2 ID3 ID3 ID3 ID5
**> > 1 2 2 3 3 3 1
**> >
**> > 'table(ids)' computes the counts, then the subscripting [ids] looks it
**> > all up.
**> >
**> > Now try it on your 40,000-long vector!
**> >
**> > Barry
*

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Jan 25 10:40:23 2006

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