Function label_currency 

pub fn label_currency(
    prefix: &str,
    suffix: &str,
    big_mark: &str,
    accuracy: Option<f64>,
) -> impl Fn(f64) -> String + Send + Sync

Sign-aware currency formatter (R’s scales::label_currency): the minus sign goes before the prefix (“-€5”, not “€-5”), thousands are grouped with big_mark (e.g. ",", ".", " ", "'"; "" disables grouping), and accuracy rounds to a multiple of it (None = up to two decimals, trailing zeros trimmed). The decimal mark is always ..

use ggplot_rs::scale::format::label_currency;
let eur = label_currency("€", "", ".", Some(1.0));
assert_eq!(eur(-1234567.0), "-€1.234.567");
let chf = label_currency("", " CHF", "'", Some(0.01));
assert_eq!(chf(9876.5), "9'876.50 CHF");