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
}

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