Plot QQ-plot using ggplot2

ggQQplot.R

ggQQplot <- function(pList, colVec = c("black", "orange", "red", "purple"),
                     legendLabel = NULL, title = "", openRange = F, sampling = 1) {

  if (is.null(legendLabel)) {
    legendLabel = colVec
  }

  if (length(pList) > length(colVec)) {
    stop("pList needs to be shorter than colVec!!!")
  }

  if (openRange) {
    pList <- lapply(pList, function(x) x[x > 0 | x < 1])
  }

  if (sampling < 1) {
    pList <- lapply(pList, function(x) sample(x, length(x) * sampling))
  }

  g <- ggplot() +
    theme_classic(base_size = 7) +
    labs(title = title,
         x = "Empirical -log<sub>10</sub> (P)",
         y = "Observed -log<sub>10</sub> (P)",) +
    theme(axis.title.x = ggtext::element_markdown(size = unit(7, "pt")),
          axis.title.y = ggtext::element_markdown(size = unit(7, "pt")),
          axis.text = element_text(size = unit(6, "pt")),
          legend.title = element_blank(),
          legend.text = element_text(size = unit(7, "pt")),
          plot.title = element_text(size = unit(8, "pt")),
          aspect.ratio = 1)

  for (i in 1:length(pList)) {
    xValue <- -log10(ppoints(length(pList[[i]])))
    yValue <- sort(-log10(pList[[i]]), decreasing = T)
    g <- g + ggrastr::geom_point_rast(mapping = aes_(x = xValue, y = yValue, col = legendLabel[i]),
                                      size = 0.1)
  }

  g <- g +
    geom_abline(slope = 1, intercept = 0, col = "red", lty = 2) +
    scale_color_manual(limits = legendLabel, values = colVec)

  return(g)
}