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
thierry.onkel...@inbo.be
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: r-help-boun...@r-project.org
> [mailto:r-help-boun...@r-project.org] Namens rajesh j
> Verzonden: maandag 6 september 2010 16:57
> Aan: r-help@r-project.org
> 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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