[R] rbind and data.frame

[james.holtman@convergys.com]

Heres some timings from a 700MHZ laptop running WIN/2000:

> x.1 <- data.frame(a=integer(85000), b=double(85000), c=character(85000))
> str(x.1)
`data.frame':   85000 obs. of  3 variables:
 $ a: int  0 0 0 0 0 0 0 0 0 0 ...
 $ b: num  0 0 0 0 0 0 0 0 0 0 ...
 $ c: Factor w/ 1 level "": 1 1 1 1 1 1 1 1 1 1 ...
#
# loading up a variable with a vector takes very little time
#
> system.time(x.1$a <- 1:85000)
[1] 0.03 0.00 0.03   NA   NA
> str(x.1)
`data.frame':   85000 obs. of  3 variables:
 $ a: int  1 2 3 4 5 6 7 8 9 10 ...
 $ b: num  0 0 0 0 0 0 0 0 0 0 ...
 $ c: Factor w/ 1 level "": 1 1 1 1 1 1 1 1 1 1 ...
#
# a 'for' loop by itself is only 0.3 seconds
#
> system.time(for (i in 1:85000)invisible(1))
[1] 0.30 0.00 0.31   NA   NA
#
# it takes me 5 seconds to initialize 85,000 of a variable, so I would
assume
# it would depend on how many and what type.  If 'factors', I would assume
you would
# declare those as 'character' and then convert to 'factor' at the end.
# so it seems fast; is there something I am missing?
#
> system.time(for (i in 1:85000) x.1$a[i] <- i)
[1] 5.12 0.04 5.22   NA   NA
>




"Liaw, Andy" <andy_liaw at merck.com>@stat.math.ethz.ch on 12/07/2001 10:32:31

Sent by:  owner-r-help at stat.math.ethz.ch


To:   r-help at stat.math.ethz.ch
cc:
Subject:  RE: [R] rbind and data.frame


Are you sure that the time difference is *only* in creating the data frame,
rather than other computations in the loop?

Andy

> -----Original Message-----
> From: Göran Broström [mailto:gb at stat.umu.se]
> Sent: Friday, December 07, 2001 7:25 AM
> To: Prof Brian Ripley
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] rbind and data.frame
>
>
> On Fri, 7 Dec 2001, Prof Brian Ripley wrote:
>
> > On Fri, 7 Dec 2001, [iso-8859-1] Göran Broström wrote:
> >
> > > On Wed, 5 Dec 2001, Göran Broström wrote:
> > >
> > > [...]
> > >
> > > > My real problem is how to create a data frame in a
> sequentially growing
> > > > manner, when I know the final size (no of cases). I
> want to avoid to
> > > > call 'rbind' many times, and instead create an 'empty'
> data frame in
> > > > one call, and then fill it. Are there better ways of doing this?
> > >
> > > Got no answer to this one, so I provide one myself:
> >
> > The usual answer is to create a data frame of the desired size and
> > populate it via indexing.  That's in some books I know!
>
> I know that book too (thanks!). I did what you suggest, and
> that took 7
> hours to run. Definitely.
>
> Göran
>
> > >
> > > The answer is: Yes, definitely. I did this, with pure  R
> code, and
> > > created a new data frame with around 58000 records. It
> took 7 hours to
> > > run. I then did it with compiled code (Fortran), and that
> made a slight
> > > difference:  It took 4.8 seconds(!).
> > >
> > > Göran
> > >
> > >
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