list files in ascending order

Question

I have a simple question about the list.files() function. I have a folder containing a list of files named in this way:

DF2.txt
DF3.txt
DF4.txt
DF5.txt
.......
.......

When I paste the following string,

files <- list.files(pattern = ".txt")

The vector returns values in this order:

"DF10.txt"
"DF11.txt"
"DF12.txt"
........
........
"DF2.txt"
"DF20.txt"
"DF21.txt"
.........
.........
"DF3.txt"
"DF30.txt"
"DF31.txt"
..........
..........

and so on. I would like to list the files in numerical increasing order as they appear in the folder. Why does R change the order of the files in the folder after list.files() and how can I rearrange these to match the original order?

Answer 1

As far as computers are concerned, it is sorting correctly. However, you can used mixedsort from the "gtools" package to get the type of sorting you want:

> myFiles <- paste("file", 1:20, ".txt", sep = "")
> sort(myFiles)
 [1] "file10.txt" "file11.txt" "file12.txt" "file13.txt" "file14.txt" "file15.txt"
 [7] "file16.txt" "file17.txt" "file18.txt" "file19.txt" "file1.txt"  "file20.txt"
[13] "file2.txt"  "file3.txt"  "file4.txt"  "file5.txt"  "file6.txt"  "file7.txt" 
[19] "file8.txt"  "file9.txt" 
> library(gtools)
> mixedsort(sort(myFiles))
 [1] "file1.txt"  "file2.txt"  "file3.txt"  "file4.txt"  "file5.txt"  "file6.txt" 
 [7] "file7.txt"  "file8.txt"  "file9.txt"  "file10.txt" "file11.txt" "file12.txt"
[13] "file13.txt" "file14.txt" "file15.txt" "file16.txt" "file17.txt" "file18.txt"
[19] "file19.txt" "file20.txt"

With your example, that means you can do:

files <- list.files(pattern = ".txt")
library(gtools)
files <- mixedsort(files)

---

User functions are fun

Since it's easy to write little utility functions, you can also write a little function like this:

ListFiles <- function(pattern = ".txt") {
  require(gtools)
  myFiles <- list.files(pattern = pattern, )
  mixedsort(myFiles)
}

Then, compare:

list.files(pattern = ".txt")
ListFiles(pattern = ".txt")

Answer 2

This is a naturalsort vs alphabetical sort problem. For me the package called naturalsort works best for displaying filenames in a human readable way.

> #install.packages("naturalsort")
> library("naturalsort")
> x <-  paste(c("2file1","2file2","10file1.2","10file0.2","20file1","100",""))
> naturalsort(x)
[1] ""          "2file1"    "2file2"    "10file0.2" "10file1.2" "20file1"   "100"   

Answer 3

The numbers are sorted alphabetically. For a base R approach you could do something like:

dat = sort(paste("DF", 1:100, ".txt", sep = ""))
numbers = as.numeric(regmatches(dat, regexpr("[0-9]+", dat)))
dat[order(numbers)]
  [1] "DF1.txt"   "DF2.txt"   "DF3.txt"   "DF4.txt"   "DF5.txt"   "DF6.txt"  
  [7] "DF7.txt"   "DF8.txt"   "DF9.txt"   "DF10.txt"  "DF11.txt"  "DF12.txt" 
 [13] "DF13.txt"  "DF14.txt"  "DF15.txt"  "DF16.txt"  "DF17.txt"  "DF18.txt" 
 [19] "DF19.txt"  "DF20.txt"  "DF21.txt"  "DF22.txt"  "DF23.txt"  "DF24.txt" 
 [25] "DF25.txt"  "DF26.txt"  "DF27.txt"  "DF28.txt"  "DF29.txt"  "DF30.txt" 
 [31] "DF31.txt"  "DF32.txt"  "DF33.txt"  "DF34.txt"  "DF35.txt"  "DF36.txt" 
 [37] "DF37.txt"  "DF38.txt"  "DF39.txt"  "DF40.txt"  "DF41.txt"  "DF42.txt" 
 [43] "DF43.txt"  "DF44.txt"  "DF45.txt"  "DF46.txt"  "DF47.txt"  "DF48.txt" 
 [49] "DF49.txt"  "DF50.txt"  "DF51.txt"  "DF52.txt"  "DF53.txt"  "DF54.txt" 
 [55] "DF55.txt"  "DF56.txt"  "DF57.txt"  "DF58.txt"  "DF59.txt"  "DF60.txt" 
 [61] "DF61.txt"  "DF62.txt"  "DF63.txt"  "DF64.txt"  "DF65.txt"  "DF66.txt" 
 [67] "DF67.txt"  "DF68.txt"  "DF69.txt"  "DF70.txt"  "DF71.txt"  "DF72.txt" 
 [73] "DF73.txt"  "DF74.txt"  "DF75.txt"  "DF76.txt"  "DF77.txt"  "DF78.txt" 
 [79] "DF79.txt"  "DF80.txt"  "DF81.txt"  "DF82.txt"  "DF83.txt"  "DF84.txt" 
 [85] "DF85.txt"  "DF86.txt"  "DF87.txt"  "DF88.txt"  "DF89.txt"  "DF90.txt" 
 [91] "DF91.txt"  "DF92.txt"  "DF93.txt"  "DF94.txt"  "DF95.txt"  "DF96.txt" 
 [97] "DF97.txt"  "DF98.txt"  "DF99.txt"  "DF100.txt"