Padding integers for use in filenames

If you’ve ever written code that generates a whole whack of files, you may have came across the following problem when processing them. Using a naming convention wherein files are numbered will  gum up any ordering which is based on string sorting (ls, for example). What you end up with is something like this:

results10.txt
results11.txt
results12.txt
results1.txt
results2.txt
...

Which is just no good, no good at all. A solution to this is to pad the file number with zeros, like so:

results0001.txt
results0002.txt
...
results0010.txt

I wrote a little function to make this easy:

pad_int<-function(n,scale){
  out_string<-paste(10*scale + n,sep='')
  out_string<-substr(out_string,2,nchar(out_string))
  return(out_string)
}

*EDIT: Very soon after posting this, ggplot creator and general rstats rockstar Hadley Wickham noted on twitter that you can do this in one line using:

sprintf(“%03d”, 1)

Then, simply pass this function your file number (n) and the number of zeros that you’d like to pad it with (scale). This should be the order of magnitude of the number of files you’re creating. For example:

for(i in 1:1000){
  padded<-pad_int(i,1000)
  file_name<-paste('results_',padded,'.txt',sep='')
  print(file_name)
}

This little bit of code came in quite handy in generating this video of dispersal on a discrete lattice. Enjoy!