But If I do that how will I resize later?
On Mon, Sep 6, 2010 at 8:54 PM, ONKELINX, Thierry
<[email protected]>wrote:
> This will give a matrix with 0 rows.
>
> data.frame(matrix(nrow = 0, ncol = 22, dimnames = list(NULL,
> LETTERS[1:22])))
>
> But you should avoid growing dataframes is the final dataframe is going
> to be large. You are very likely to get memory problems. It is much to
> better to create a large enough dataframe and then overwrite the rows.
> And it is faster too...
>
> > nrows <- 2000
> > ncols <- 22
> > system.time({
> + tmp <- data.frame(matrix(nrow = 0, ncol = ncols))
> + for(i in seq_len(nrows)){
> + tmp <- rbind(tmp, rnorm(ncols))
> + }
> + })
> user system elapsed
> 7.83 0.02 7.86
> > system.time({
> + tmp <- data.frame(matrix(nrow = nrows, ncol = ncols))
> + for(i in seq_len(nrows)){
> + tmp[i, ] <- rnorm(ncols)
> + }
> + })
> user system elapsed
> 3.75 0.00 3.76
>
> #In this case an apply construction was even faster
>
> > system.time({
> + tmp <- t(sapply(seq_len(nrows), function(i){
> + rnorm(ncols)
> + }))
> + })
> user system elapsed
> 0.02 0.00 0.02
>
>
>
>
> ------------------------------------------------------------------------
> ----
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek
> team Biometrie & Kwaliteitszorg
> Gaverstraat 4
> 9500 Geraardsbergen
> Belgium
>
> Research Institute for Nature and Forest
> team Biometrics & Quality Assurance
> Gaverstraat 4
> 9500 Geraardsbergen
> Belgium
>
> tel. + 32 54/436 185
> [email protected]
> www.inbo.be
>
> To call in the statistician after the experiment is done may be no more
> than asking him to perform a post-mortem examination: he may be able to
> say what the experiment died of.
> ~ Sir Ronald Aylmer Fisher
>
> The plural of anecdote is not data.
> ~ Roger Brinner
>
> The combination of some data and an aching desire for an answer does not
> ensure that a reasonable answer can be extracted from a given body of
> data.
> ~ John Tukey
>
>
> > -----Oorspronkelijk bericht-----
> > Van: [email protected]
> > [mailto:[email protected]] Namens rajesh j
> > Verzonden: maandag 6 september 2010 16:57
> > Aan: [email protected]
> > Onderwerp: [R] rbind() overwriting data.frame()
> >
> > Hi,
> >
> > first off, I wanna ask how do I declare a data.frame of 0
> > rows and n columns?
> >
> > Coming to my problem,
> >
> > I have a data.frame of 22 columns by dynamic rows which I
> > insert using rbind. The total number of rows could go upto
> > 2,00,000. The problem is that after about 800 or 900 get
> > inserted rbind starts overwriting the data.frame and I end up
> > with a total of 800-900 rows. What is up with that?
> > The 22 columns are all strings each having about 10 characters
> > --
> > Rajesh.J
> >
> > [[alternative HTML version deleted]]
> >
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> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
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--
Rajesh.J
[[alternative HTML version deleted]]
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