R/geom_split_violin.R

In soniamitchell/SpARKjags:

#' https://stackoverflow.com/questions/35717353/split-violin-plot-with-ggplot2

GeomSplitViolin <- ggproto(
  "GeomSplitViolin",
  GeomViolin,
  draw_group = function(self, data, ...,
                        draw_quantiles = NULL) {
    data <- transform(data, xminv = x - violinwidth * (x - xmin),
                      xmaxv = x + violinwidth * (xmax - x))
    grp <- data[1, "group"]
    newdata <- plyr::arrange(transform(data,
                                       x = if (grp %% 2 == 1) xminv else xmaxv),
                             if (grp %% 2 == 1) y else -y)
    newdata <- rbind(newdata[1, ], newdata, newdata[nrow(newdata), ],
                     newdata[1, ])
    newdata[c(1, nrow(newdata) - 1, nrow(newdata)), "x"] <- round(newdata[1, "x"])

    if (length(draw_quantiles) > 0 & !scales::zero_range(range(data$y))) {
      stopifnot(all(draw_quantiles >= 0), all(draw_quantiles <=
                                                1))
      quantiles <- ggplot2:::create_quantile_segment_frame(data, draw_quantiles)
      aesthetics <- data[rep(1, nrow(quantiles)),
                         setdiff(names(data), c("x", "y")), drop = FALSE]
      aesthetics$alpha <- rep(1, nrow(quantiles))
      both <- cbind(quantiles, aesthetics)
      quantile_grob <- GeomPath$draw_panel(both, ...)
      ggplot2:::ggname("geom_split_violin",
                       grid::grobTree(GeomPolygon$draw_panel(newdata, ...),
                                      quantile_grob))
    }
    else {
      ggplot2:::ggname("geom_split_violin",
                       GeomPolygon$draw_panel(newdata, ...))
    }
  })

geom_split_violin <- function(mapping = NULL, data = NULL, stat = "ydensity",
                              position = "identity", ...,
                              draw_quantiles = NULL, trim = TRUE,
                              scale = "area", na.rm = FALSE,
                              show.legend = NA, inherit.aes = TRUE) {
  layer(data = data, mapping = mapping, stat = stat, geom = GeomSplitViolin,
        position = position, show.legend = show.legend,
        inherit.aes = inherit.aes,
        params = list(trim = trim, scale = scale,
                      draw_quantiles = draw_quantiles, na.rm = na.rm, ...))
}