Centre a ggplot legend beneath the plot using cowplot

Extract the legend from a ggplot object and place it centred beneath the whole plot. (As opposed to centred under the axis area only.) If the cowplot package is not installed, the plot is returned unchanged.

Usage

centre_legend_below(p, rel_heights = c(1, 0.1))

Arguments

p

A ggplot object whose legend should be centred beneath the plot.

rel_heights

A numeric vector of length two giving the relative heights of the plot area and the legend area when stacked vertically. Defaults to c(1, 0.1), which gives the legend 10% of the vertical space the plot gets.

Value

If cowplot is installed, a cowplot object with the legend centred underneath the plot. Otherwise, the original ggplot object is returned unchanged.

Details

This function extracts the legend from the supplied ggplot object, removes the legend from the plot itself, and then stacks the plot and legend vertically using cowplot::plot_grid(). The relative heights of the two components can be controlled via rel_heights.

Examples

if (FALSE) { # \dontrun{
  p <- ggplot2::ggplot(mtcars, ggplot2::aes(factor(cyl), mpg, fill = factor(cyl))) +
    ggplot2::geom_col()
  centre_legend_below(p)
} # }