label_number() argument to always print number with sign

[davidchall]

Currently, label_number() only prints negative numbers with a sign. I'm requesting an argument to force a + symbol before positive numbers.

> scales::label_number()(seq(-1, 1, 0.5))
[1] "-1.00" "-0.50" "0.00"  "0.50"  "1.00"

The base R format() method doesn't provide an argument for this, so it's not currently possible to achieve this with dot args. Probably it would need to be added in post-processing between these lines (i.e. before adding a prefix):

scales/R/label-number.r

Lines 154 to 163 in 1e2c918

	ret <- format(
	scale * x,
	big.mark = big.mark,
	decimal.mark = decimal.mark,
	trim = trim,
	nsmall = nsmall,
	scientific = FALSE,
	...
	)
	ret <- paste0(prefix, ret, suffix)

One open question is whether zero should get +, - or nothing? The sprintf() function suggests that we should use +. This is also consistent with Python and C.

So I think I'm suggesting something like:

ret <- ifelse(x >= 0, paste0("+", ret), ret)

[dirkschumacher]

Happy to help here and send the PR. I see at least two options.

1. Add a new parameter e.g. show_plus_sign = FALSE that controls the plus sign

scales::label_number(show_plus_sign = TRUE)(seq(-1, 1, 0.5))

2. Allow suffix and prefix to be either a character or function taking the original vector values . Then one can build such a formatter outside the package. In addition scales could provide a prefix function that adds a + in front of a positive number.

plus_sign <- function(x) ifelse(x >= 0, "+", "")
scales::label_number(prefix = plus_sign)(seq(-1, 1, 0.5))

Both options would be backwards compatible. Any other ideas or preferences?

[davidchall]

Hi @dirkschumacher - thanks for your offer of help!

I think these are both good options. I have a strong preference for (1), because showing a plus sign is quite a universal concept (i.e. independent of the prefix or suffix). But I'd definitely like to get feedback from the package maintainers before opening a PR.

As is often the case, naming this new argument is probably the most difficult bit. Here are some ideas:

• show_plus_sign
• always_sign (following documentation of sprintf(): "Always print number with sign: by default only negative numbers are printed with a sign.")
• both_sign