R/sm_common_legend.R

In smin95/sesplot: Creating Standalone and Composite Plots in 'ggplot2' for Publications

#' Creating a common legend for subplots on a separate panel
#'
#' @param x
#' Location of the legend along the x-axis. Default is the middle origin (0.5).
#' @param y
#' Location of the legend along the y-axis. Default is the middle origin (0.5).
#' @param title
#' Title of the legend. Input should be string
#' @param direction
#' Direction of the legend: 'horizontal' or 'vertical'.
#' @param border
#' If set TRUE, border around the legend will be created.
#' If set FALSE, the border will be removed.
#' @param legend_spacing
#' Spacing within the legend.
#' @param border_color
#' Color of the legend border
#' @param textRatio
#' Size of the text relative to the plot's default. It has been set to 1.2. The larger
#' the textRatio, the larger the texts in the legend.
#'
#' @return
#' It prints a legend on a blank plot. It can be used to create
#' a common legend for subplots.
#' @export
#'
#' @importFrom cowplot theme_nothing
#'
#' @examples
#' library(ggplot2)
#' library(smplot2)
#' ggplot(data = mtcars, mapping = aes(x = drat, y = mpg,
#' fill = as.factor(cyl))) +
#'  geom_point(shape = 21, color = 'white', size = 3) +
#'  sm_common_legend(x = .5, y = 0.5 , direction='horizontal',
#'                   border=FALSE)
#'

sm_common_legend <- function(x = 0.5, y = 0.5, title=FALSE, direction='vertical',
                             border=TRUE, legend_spacing = 0.5, border_color='black',
                             textRatio = 1) {

  blank <- do.call('annotate', list(geom = 'rect', ymin=-Inf,ymax=Inf,xmin=-Inf,xmax=Inf,
                                                       fill = 'white'))
  blank2 <- theme_nothing()
  box <- do.call('theme', list(legend.spacing.y = unit(legend_spacing, "mm"),
                                                  legend.spacing.x = unit(legend_spacing, 'mm'),
                                                  aspect.ratio = 1,
                                                  legend.background = element_blank(),
                                                  legend.box.background = element_rect(colour = border_color)))

  if (title==TRUE) {
    location <- do.call('theme',  list(legend.position = c(x,y), legend.direction = direction,
                                       legend.text = element_text(size = rel(textRatio)),
                                       legend.title = element_text(size = rel(textRatio))))
  } else {
    location <- do.call('theme', list(legend.position = c(x,y),legend.direction = direction,
                                      legend.text = element_text(size = rel(textRatio)),
                                                         title = element_blank()))
  }

  if (border==FALSE) {
    box <- NULL
  }

  list(blank, blank2, location, box)
}