About populating a dataframe in a loop
As a rule never rbind in a loop. It has O(n^2) run time because the rbind
itself can be O(n) (where n is the number of data.frames). Instead either
put them all into a list with lapply or vector("list", length=) and then
datatable::rbindlist, do.call(rbind, thelist) or use the equivalent from
dplyr. All of which will be much more efficient.
On Fri, Jan 6, 2017 at 8:46 PM, lily li <chocold12 at gmail.com> wrote:
Hi Rui, Thanks for your reply. Yes, when I tried to rbind two dataframes, it works. However, if there are more than 50, it got stuck for hours. When I tried to terminate the process and open the csv file separately, it has only one data frame. What is the problem? Thanks. On Fri, Jan 6, 2017 at 11:12 AM, Rui Barradas <ruipbarradas at sapo.pt> wrote:
Hello,
Works with me:
set.seed(6574)
pre.mat = data.frame()
for(i in 1:10){
mat.temp = data.frame(x = rnorm(5), A = sample(LETTERS, 5, TRUE))
pre.mat = rbind(pre.mat, mat.temp)
}
nrow(pre.mat) # should be 50
Can you give us an example that doesn't work?
Rui Barradas
Em 06-01-2017 18:00, lily li escreveu:
Hi R users,
I have a question about filling a dataframe in R using a for loop.
I created an empty dataframe first and then filled it, using the code:
pre.mat = data.frame()
for(i in 1:10){
mat.temp = data.frame(some values filled in)
pre.mat = rbind(pre.mat, mat.temp)
}
However, the resulted dataframe has not all the rows that I desired for.
What is the problem and how to solve it? Thanks.
[[alternative HTML version deleted]]
______________________________________________ R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posti ng-guide.html and provide commented, minimal, self-contained, reproducible code.
[[alternative HTML version deleted]]
______________________________________________ R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/ posting-guide.html and provide commented, minimal, self-contained, reproducible code.