formatting - How to format a number as percentage in R?

Question

One of the things that used to perplex me as a newby to R was how to format a number as a percentage for printing.

For example, display 0.12345 as 12.345%. I have a number of workarounds for this, but none of these seem to be "newby friendly". For example:

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

paste(round(100*m, 2), "%", sep="")
[1] "26.55%" "37.21%" "57.29%" "90.82%" "20.17%"

sprintf("%1.2f%%", 100*m)
[1] "26.55%" "37.21%" "57.29%" "90.82%" "20.17%"

Question: Is there a base R function to do this? Alternatively, is there a widely used package that provides a convenient wrapper?

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Despite searching for something like this in ?format, ?formatC and ?prettyNum, I have yet to find a suitably convenient wrapper in base R. ??"percent" didn't yield anything useful. library(sos); findFn("format percent") returns 1250 hits - so again not useful. ggplot2 has a function percent but this gives no control over rounding accuracy.

Answer 1

Even later:

As pointed out by @DzimitryM, percent() has been "retired" in favor of label_percent(), which is a synonym for the old percent_format() function.

label_percent() returns a function, so to use it, you need an extra pair of parentheses.

library(scales)
x <- c(-1, 0, 0.1, 0.555555, 1, 100)
label_percent()(x)
## [1] "-100%"   "0%"      "10%"     "56%"     "100%"    "10 000%"

Customize this by adding arguments inside the first set of parentheses.

label_percent(big.mark = ",", suffix = " percent")(x)
## [1] "-100 percent"   "0 percent"      "10 percent"    
## [4] "56 percent"     "100 percent"    "10,000 percent"

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An update, several years later:

These days there is a percent function in the scales package, as documented in krlmlr's answer. Use that instead of my hand-rolled solution.

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Try something like

percent <- function(x, digits = 2, format = "f", ...) {
  paste0(formatC(100 * x, format = format, digits = digits, ...), "%")
}

With usage, e.g.,

x <- c(-1, 0, 0.1, 0.555555, 1, 100)
percent(x)

(If you prefer, change the format from "f" to "g".)