[R] Optimize code to read text-file with digits

[Martin Møller Skarbiniks Pedersen]

Hi,

  Every day I try to write some small R programs to improve my R-skills.
  Yesterday I wrote a small program to read the digits from "A Million
Random Digits" from RAND.
  My code works but it is very slow and I guess the code is not optimal.

The digits.txt file downloaded from
https://www.rand.org/pubs/monograph_reports/MR1418.html
contains 20000 lines which looks like this:
00000   10097 32533  76520 13586  34673 54876  80959 09117  39292 74945
00001   37542 04805  64894 74296  24805 24037  20636 10402  00822 91665
00002   08422 68953  19645 09303  23209 02560  15953 34764  35080 33606
00003   99019 02529  09376 70715  38311 31165  88676 74397  04436 27659
00004   12807 99970  80157 36147  64032 36653  98951 16877  12171 76833

My program which is slow looks like this:

filename <- "digits.txt"
lines <- readLines(filename)

numbers <- vector('numeric')
for (i in 1:length(lines)) {

    # remove first column
    lines[i] <- sub("[^ ]+ +","",lines[i])

    # remove spaces
    lines[i] <- gsub(" ","",lines[i])

    # split the characters and convert them into numbers
    numbers <- c(numbers,as.numeric(unlist(strsplit(lines[i],""))))
}

Thanks for any advice how this program can be improved.

Regards
Martin M. S. Pedersen

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