R/sm_add_legend.R

In smin95/sesR: Create Standalone and Composite Plots in 'ggplot2' for Publications

#' Adding a common legend on a combined figure
#'
#' @param combined_plot
#' Combined figure, an output from sm_put_together().
#' @param x
#' Location of the legend along the x-axis of the combined figure. The middle origin is at 0.5.
#' @param y
#' Location of the legend along the y-axis of the combined figure. The middle origin is at 0.5.
#' @param sampleplot
#' A variable containing one sample ggplot2 from which the legend can be derived.
#' @param legend
#' Pre-specified layer of legend created with sm_common_legend().
#' @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 font_size
#' Text size of the legend
#' @importFrom patchwork inset_element
#'
#' @return
#' It prints a legend on a a combined plot. It can be used to create
#' a common legend for subplots.
#' @export
#'
#' @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_classic(legends = FALSE) -> p1
#'
#' ggplot(data = mtcars, mapping = aes(
#'   x = drat, y = mpg,
#'   fill = as.factor(cyl)
#' )) +
#'   geom_point(
#'     shape = 21, color = "white",
#'     size = 3
#'   ) +
#'   sm_hvgrid(legends = FALSE) -> p2
#'
#' combined_fig <- sm_put_together(list(p1, p2), ncol = 2, nrow = 1)
#' sm_add_legend(combined_fig, x = 0.1, y = 0.1, sampleplot = p1)
#'
sm_add_legend <- function(combined_plot, x, y, sampleplot, legend, direction = "vertical",
                          border = TRUE, legend_spacing = 0.5, border_color = "black",
                          font_size = 12) {
  if (missing(legend)) {
    if (missing(sampleplot)) {
      stop("If legend is not provided, sampleplot should be provided so that a legend can be derived.")
    }

    poi <- sampleplot + sm_hgrid(legends = TRUE) + theme(legend.direction = direction) +
      theme(
        legend.spacing.y = unit(legend_spacing, "mm"),
        legend.spacing.x = unit(legend_spacing, "mm"),
        aspect.ratio = 1,
        legend.background = element_blank(),
        legend.text = element_text(size = font_size),
        legend.title = element_text(size = font_size)
      )

    if (border == TRUE) {
      poi <- poi + theme(legend.box.background = element_rect(colour = border_color))
    } else {
      poi <- poi
    }

    tmp <- ggplot_gtable(ggplot_build(poi))
    leg <- which(sapply(tmp$grobs, function(x) x$name) == "guide-box")
    legend <- tmp$grobs[[leg]]
  } else if (missing(sampleplot)) {
    sampleplot <- NULL
  }
  if (x > 0.99) x <- 0.99
  if (y > 0.99) y <- 0.99


  output <- ggdraw(combined_plot + inset_element(legend, x, y, x, y))
  return(output)
}