Get limits spanning a set of values that are symmetric about a central value

This is useful for making the axis range of a plot symmetric about a key central value.

Usage

sym_limits(values, transform = "identity", center = NULL)

Arguments

values: Vector of values.
transform: Transformation to apply to the values. Passed to scales::as.transform(). Default "identity".
center: Custom center value for the span on the untransformed scale. If not specified, the span will be centered at 0 on the transformed scale.

Value

a length-two vector whose entries are symmetric about center on the transformed scale and span the range of values.

Details

Given a center point center and a set of values values, returns c(center - x, center + x) where x is the entry of values that is farthest from center (i.e. x <- max(abs(values - center))) on the transformed scale.

If a custom center point is not specified, sym_limits() centers values around 0 on the transformed scale.

Examples

sym_limits(c(-5.1, 2.2, 7.1))
#> [1] -7.1  7.1

# centered at 1, which corresponds to 0 on the
# transformed scale
sym_limits(values = c(0.4, 10), transform = "log10")
#> [1]  0.1 10.0

sym_limits(values = c(2, 9), transform = "sqrt", center = 4)
#> [1] 1 9

library(ggplot2)
library(tibble)
data <- tibble(x = 1:5, y = rnorm(5, mean = 2))
plot <- ggplot(
    data = data,
    mapping = aes(x = x, y = y)) +
    geom_hline(yintercept = 2, size = 2, linetype = "dashed") +
    geom_point(size = 4) +
    coord_cartesian(ylim = sym_limits(data$y, center = 2)) +
    theme_forecasttools()
#> Warning: Using `size` aesthetic for lines was deprecated in ggplot2 3.4.0.
#> ℹ Please use `linewidth` instead.
plot


data_log <- tibble(x = 1:5, y = 10^rnorm(5))
plot_log <- ggplot(
    data = data_log,
    mapping = aes(x = x, y = y)) +
    geom_hline(yintercept = 1, size = 2, linetype = "dashed") +
    geom_point(size = 4) +
    scale_y_continuous(transform = "log10") +
    coord_cartesian(ylim = sym_limits(data_log$y, transform = "log10")) +
    theme_forecasttools()
plot_log