About populating a dataframe in a loop

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.

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