[R] About populating a dataframe in a loop

[lily li]

Thanks, Richard. But if the data cannot fill the constructed data frame,
will there be NA values?


On Fri, Jan 6, 2017 at 10:07 PM, Richard M. Heiberger <rmh at temple.edu>
wrote:

> Incrementally increasing the size of an array is not efficient in R.
> The recommended technique is to allocate as much space as you will
> need, and then fill it.
>
> > system.time({tmp <- 1:5 ; for (i in 1:1000) tmp <- rbind(tmp, 1:5)})
>    user  system elapsed
>   0.011   0.000   0.011
> > dim(tmp)
> [1] 1001    5
> > system.time({tmp <- matrix(NA, 1001, 5); for (i in 1:1001) tmp[i,] <-
> 1:5})
>    user  system elapsed
>   0.001   0.000   0.001
> > dim(tmp)
> [1] 1001    5
>
> On Fri, Jan 6, 2017 at 11:46 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]]
> >>>
> >>> ______________________________________________
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> >>> 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.
>

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