R/csvSample.R

In duncantl/FastCSVSample: Fast sampling of lines of (any) text file

#@example  tt = csvSample("~/Data/Airline/Airlines/2002.csv", 100)
#          read.csv(textConnection(tt), header = FALSE)
csvSample =
function(file, n, rows = sample(1:numRows, n),
         numRows = getNumLines(file),
         randomize = FALSE, header = TRUE)
{
   file = path.expand(file)
   if(!file.exists(file))
       stop("file does not exist")

   rows = sort(as.integer(rows))
   if(header)
     rows = rows + 1L

   ans = .Call("R_csv_sample", file, rows)

   names(ans) = rows
   
   if(randomize)
      sample(ans)
   else
      ans
}

getNumLines =
function(file)
{
   txt = system(sprintf("wc -l %s", file), intern = TRUE)
   as.integer(gsub("^[[:space:]]*([0-9]+) .*", "\\1", txt))
}