[r] Formatting Decimal places in R

I have a number, for example 1.128347132904321674821 that I would like to show as only two decimal places when output to screen (or written to a file). How does one do that?

x <- 1.128347132904321674821

EDIT:

The use of:

options(digits=2)

Has been suggested as a possible answer. Is there a way to specify this within a script for one-time use? When I add it to my script it doesn't seem to do anything different and I'm not interested in a lot of re-typing to format each number (I'm automating a very large report).

--

Answer: round(x, digits=2)

The function formatC() can be used to format a number to two decimal places. Two decimal places are given by this function even when the resulting values include trailing zeros.

If you prefer significant digits to fixed digits then, the signif command might be useful:

> signif(1.12345, digits = 3)
[1] 1.12
> signif(12.12345, digits = 3)
[1] 12.1
> signif(12345.12345, digits = 3)
[1] 12300

I'm using this variant for force print K decimal places:

# format numeric value to K decimal places
formatDecimal <- function(x, k) format(round(x, k), trim=T, nsmall=k)

You can format a number, say x, up to decimal places as you wish. Here x is a number with many decimal places. Suppose we wish to show up to 8 decimal places of this number:

x = 1111111234.6547389758965789345
y = formatC(x, digits = 8, format = "f")
# [1] "1111111234.65473890"

Here format="f" gives floating numbers in the usual decimal places say, xxx.xxx, and digits specifies the number of digits. By contrast, if you wanted to get an integer to display you would use format="d" (much like sprintf).

if you just want to round a number or a list, simply use

round(data, 2)

Then, data will be round to 2 decimal place.

Something like that :

options(digits=2)

Definition of digits option :

digits: controls the number of digits to print when printing numeric values.

here's my approach from units to millions. digits parameter let me adjust the minimum number of significant values (integer + decimals). You could adjust decimal rounding inside first.

number <-function(number){
  result <- if_else(
    abs(number) < 1000000,
    format(
      number, digits = 3,
      big.mark = ".",
      decimal.mark = ","
    ),
    paste0(
      format(
        number/1000000,
        digits = 3,
        drop0trailing = TRUE,
        big.mark = ".",
        decimal.mark = ","
      ),
      "MM"
    )
  )
  # result <- paste0("$", result)
  return(result)
}

Note that numeric objects in R are stored with double precision, which gives you (roughly) 16 decimal digits of precision - the rest will be noise. I grant that the number shown above is probably just for an example, but it is 22 digits long.

Check functions prettyNum, format

to have trialling zeros (123.1240 for example) use sprintf(x, fmt='%#.4g')

Looks to me like to would be something like

library(tutoR)
format(1.128347132904321674821, 2)

Per a little online help.

You can try my package formattable.

> # devtools::install_github("renkun-ken/formattable")
> library(formattable)
> x <- formattable(1.128347132904321674821, digits = 2, format = "f")
> x
[1] 1.13

The good thing is, x is still a numeric vector and you can do more calculations with the same formatting.

> x + 1
[1] 2.13

Even better, the digits are not lost, you can reformat with more digits any time :)

> formattable(x, digits = 6, format = "f")
[1] 1.128347

for 2 decimal places assuming that you want to keep trailing zeros

sprintf(5.5, fmt = '%#.2f')

which gives

[1] "5.50"

As @mpag mentions below, it seems R can sometimes give unexpected values with this and the round method e.g. sprintf(5.5550, fmt='%#.2f') gives 5.55, not 5.56