How to write a fixed-width file?

Question

I should write a txt file with a specific format based on fixed-width columns (e.g. 1st variable in the columns 1-8, 2nd variable in the columns 9-15...).

The original data have different length and they have to be put on the right of the assigned columns. For example: the values "-15.96" and "12.489" have to be written in the columns 1-8 of the first and the second line, while "-872.6" and "1723.6" in the columns 9-15. This will be:

123456789012345 (n columns)
  -15.96 -872.6
  12.489 1723.6

How could I do that with R? Now I have a simple table like this:

x <- data.frame(a= sample(-500.5:500.8,4),
                b= sample(-250.6:420.9,4))

The gdata package has a write.fwf function. See stackoverflow.com/a/50499905/2372064`. I'm surprised you didn't find that with google. — MrFlick
– MrFlick, Commented Feb 18, 2019 at 16:29

G. Grothendieck · Accepted Answer · 2019-02-18 16:50:05Z

4

Format it with sprintf (help(sprintf) for more info) and then write the lines out with writeLines. No packages are used.

filename <- stdout() # change to your file name
Lines <- with(x, sprintf("%8.2f%7.1f", a, b))
writeLines(Lines, filename)
##  -212.50  380.4
##   288.50 -220.6
##   -92.50  102.4
##   381.50  346.4

The second line could alternately be written:

Lines <- do.call("sprintf", c("%8.2f%7.1f", x))

answered Feb 18, 2019 at 16:50

G. Grothendieck

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Hao · Accepted Answer · 2019-09-24 16:16:04Z

Here is a more automated version using Grothendieck's answer

https://gist.github.com/haozhu233/28d1309b58431f4929f78243054f1f58

#' Generate fixed width file in R
#' @description This simple function creates fixed width file with no 
#' extra dependencies. 
#' @param justify "l", "r" or something like "lrl" for left, right, left. 
#' @examples dt <- data.frame(a = 1:3, b = NA, c = c('a', 'b', 'c'))
#' write_fwf(dt, "test.txt", width = c(4, 4, 3))
#' @export
write_fwf = function(dt, file, width, 
                     justify = "l", replace_na = "NA") {
  fct_col = which(sapply(dt, is.factor))
  if (length(fct_col) > 0) {
    for (i in fct_col) {
      dt[,i] <- as.character(dt[,i])
    }
  }
  dt[is.na(dt)] = replace_na
  n_col = ncol(dt)
  justify = unlist(strsplit(justify, ""))
  justify = as.character(factor(justify, c("l", "r"), c("-", "")))
  if (n_col != 1) {
    if (length(width) == 1) width = rep(width, n_col)
    if (length(justify) == 1) justify = rep(justify, n_col)
  }
  sptf_fmt = paste0(
    paste0("%", justify, width, "s"), collapse = ""
  )
  tbl_content = do.call(sprintf, c(fmt = sptf_fmt, dt))
  tbl_header = do.call(sprintf, c(list(sptf_fmt), names(dt)))
  out = c(tbl_header, tbl_content)
  writeLines(out, file)
}

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