Format numbers as power-of-10 R expressions — label

Creates a labeller function that formats numbers in scientific notation using power-of-10 R expressions (e.g., \(2.5\times 10^3\) or \(5\times 10^6\)). Useful for axis labels in ggplot2 when dealing with large numbers or when you want to emphasize the order of magnitude.

Usage

label_power10(
  decimal.mark = NULL,
  digits = 3,
  scale = 1,
  prefix = "",
  suffix = "",
  magnitude_only = FALSE,
  ...
)

Arguments

decimal.mark: Character used as decimal separator. If NULL (default), retrieves the setting from [scales::number_options()].
digits: Number of significant digits to show in the mantissa.
scale: Scaling factor multiplied to the input values. Default is 1.
prefix: Character string to prepend to each label. Default is "".
suffix: Character string to append to each label. Default is "".
magnitude_only: Logical. If TRUE, shows only the power-of-10 part (e.g., \(10^5\) instead of \(1\times 10^5\)). Default is FALSE.
...: Additional arguments passed to scales::scientific().

Value

A label function that takes a numeric vector and returns an expression vector suitable for use as axis labels in ggplot2.

Details

The function converts numbers to scientific notation and then formats them as mathematical expressions using the R expression syntax:

For exponent 0: returns the mantissa as-is (e.g., \(5.5\))
For exponent 1: it omits the exponent (e.g., \(1.5\times 10\))
For other exponents: everything is shown (e.g., \(1.5\times 10^3\))

When magnitude_only = TRUE:

For exponent 0: returns \(1\)
For exponent 1: returns \(10\)
For other exponents (positive or negative): returns \(10^{exponent}\)

The function handles negative numbers by preserving the sign and supports custom decimal marks, prefixes, and suffixes.

Examples

library(ggplot2)

# Basic usage with default settings
label_power10()(c(1000, 10000, 100000, -1000))
#> expression(1 %*% 10^3, 1 %*% 10^4, 1 %*% 10^5, -1 %*% 10^3)

# Use in ggplot2
ggplot(
  data.frame(x = 1:5, y = c(1, 50000, 75000, 100000, 200000)),
  aes(x, y)
) +
  geom_point() +
  scale_y_continuous(labels = label_power10())


# Use in ggplot2 with options
ggplot(
  data.frame(x = 1:5, y = c(1, 50000, 75000, 100000, 200000)),
  aes(x, y)
) +
  geom_point() +
  scale_y_continuous(labels = label_power10(decimal.mark = ",", digits = 2, suffix = " CFU"))


# Magnitude only for cleaner labels with log scales
ggplot(
  data.frame(x = 1:5, y = c(1000, 10000, 100000, 1000000, 10000000)),
  aes(x, y)
) +
  geom_point() +
  scale_y_log10(labels = label_power10(magnitude_only = TRUE))