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Editorial Team
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Asked: 2026-05-24T21:43:52+00:00

In a previous question , I asked whether whether a convenient wrapper exists inside

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In a previous question, I asked whether whether a convenient wrapper exists inside base R to format numbers as percentages.

This elicited three responses:

  1. Probably not.
  2. Such a wrapper would be too narrow to be useful. It is better that useRs learn how to use existing tools, such as sprintf, which can format numbers in a highly flexible way.
  3. Such a wrapper is problematic, anyway, since you lose the ability to perform calculations on the object.

Still, in my view the sprintf function is just a little bit too obfuscated for the R beginner to learn (except if they come from a C background). Perhaps a better solution is to modify format or prettyNum to have options for adding prefixes and suffixes, so you could easily create percents, currencies, degrees, etc.

Question:

How would you design a function, class or set of functions to elegantly deal with formatting numbers as percentages, currencies, degrees, etc?

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1 Answer

  1. Editorial Team

    I would probably keep things very simple. format() is generally useful for most basic formatting needs. I would extend that with a simple wrapper that allowed arbitrary prefix and suffix strings. Here is a simple version:

    formatVal <- function(x, prefix = "", suffix = "", sep = "", collapse = NULL,
                      ...) {
    x <- format(x, ...)
    x <- paste(prefix, x, suffix, sep = sep, collapse = collapse)
    x
}

    If I were doing this for real, I would probably not have the collapse argument in the definition of formatVal(), but instead process it out of ..., but for illustration I kept the above function simple.

    Using:

    set.seed(1)
m <- runif(5)

    some simple examples of usage

    > formatVal(m*100, suffix = "%")
[1] "26.55087%" "37.21239%" "57.28534%" "90.82078%" "20.16819%"
> formatVal(m*100, suffix = "%", digits = 2)
[1] "27%" "37%" "57%" "91%" "20%"
> formatVal(m*100, suffix = "%", digits = 2, nsmall = 2)
[1] "26.55%" "37.21%" "57.29%" "90.82%" "20.17%"
> formatVal(m, prefix = "£")
[1] "£0.2655087" "£0.3721239" "£0.5728534" "£0.9082078" "£0.2016819"
> formatVal(m, prefix = "£", digits = 1)
[1] "£0.3" "£0.4" "£0.6" "£0.9" "£0.2"
> formatVal(m, prefix = "£", digits = 1, nsmall = 2)
[1] "£0.27" "£0.37" "£0.57" "£0.91" "£0.20"
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