[R] About populating a dataframe in a loop

[Richard M. Heiberger]

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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>>> 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.