a performance benchmark for https://github.com/Rdatatable/data.table/pull/1613

fwrite-performance-test.R

library(data.table)
library(microbenchmark)

performanceTest <- function (nrows=100000, ncols=400, quote=TRUE, col.type='character') {
  
  message(paste0('generating test table, col type ', col.type))
  x <- c(1:nrows)
  dt <- data.table(col1=x)
  
  col_generators = list(
    character = function(x) paste0('char', x),
    double = function(x) as.double(x / 0.9),
    integer = function(x) x,
    factor = function(x) as.factor(paste0('factor', x %% 1000))
  )
  
  if (col.type != 'mixed') {
    col_generators <- col_generators[col.type]
  }
  
  for (col in c(1:ncols)) {
    col_generator <- col_generators[[((col-1) %% length(col_generators))+1]]
    dt[, (paste0('col', col)) := col_generator(x)]
  }
  
  message(paste0('dt of size ', nrow(dt), 'x', ncol(dt), ' quoting ', quote))
  
  timeIt <- function(func) {
    f <- tempfile()
    t0 <- get_nanotime()
    func(dt, f)
    time_diff <- (get_nanotime() - t0) * 1e-9
    file.remove(f)
    time_diff
  }
  
  alternatives = list(
    fwrite = function(dt, f) {
      fwrite(dt, f, quote=quote)
    },
    write.csv = function(dt, f) {
      write.csv(dt, f, quote=quote, row.names=FALSE)
    }
  )
  
  n_rounds <- 3
  
  results <- rbindlist(
    lapply(1:n_rounds,
       function (i) {
         round <- list()
         for (alt in names(alternatives)) {
           message(alt, ' ', i)
           round[[alt]] <- timeIt(alternatives[[alt]])
         }
         round
       }
    )
  )
  
  means <- results[, lapply(.SD, mean)][, lapply(.SD, as.numeric)]
  fwrite_time <- means[, fwrite]
  speedup <- means[, write.csv] / fwrite_time
  list(speedup=speedup, fwrite_time=fwrite_time)
}

performanceTable <- function() {
  tab <- data.table(expand.grid(list(
      `col.type` = c('character', 'double', 'integer', 'factor', 'mixed'),
      `quote` = c(TRUE, FALSE)
  )))
  
  for (j in 1:nrow(tab)) {
    r <- performanceTest(col.type=tab[j, `col.type`], quote=tab[j, `quote`])
    tab[j, speedup := r$speedup]
    tab[j, fwrite_time := r$fwrite_time]
  }
  
  tab
}

@oseiskar Sys.time() won't time nicely, for a reason why see gc argument ?system.time.

Ran again with this version:

col.type	quote	speedup	fwrite_time (s)
character	TRUE	2.03	8.941
double	TRUE	3.27	17.885
integer	TRUE	4.33	4.943
factor	TRUE	2.31	8.409
mixed	TRUE	2.99	10.181
character	FALSE	2.15	7.594
factor	FALSE	2.33	7.643
mixed	FALSE	3.027	9.749

Updated code to use microbenchmark::get_nanotime() (thanks @MichaelChirico ).
Results are similar.

col.type	quote	speedup	fwrite_time (s)
character	TRUE	2.00	8.91
double	TRUE	3.25	17.85
integer	TRUE	4.35	4.92
factor	TRUE	2.21	8.5
mixed	TRUE	2.91	10.31
character	FALSE	2.17	7.57
factor	FALSE	2.30	7.75
mixed	FALSE	3.03	9.68