ggplot2 在绘图区域外添加小刻度线而不关闭剪辑

Question

我正在寻找一种在不使用 coord_cartesian(clip = "off") 的情况下向 ggplots 添加次要刻度线的方法。或者一种可重现地将裁剪应用于 x 轴而不是 y 轴的方法，反之亦然。

到目前为止，我一直在使用这个出色的答案 here 中定义的 annotation_ticks() 函数和 GeomTicks geom（进行了一些小的修改以使其与 ggplot2 v3.3.0 一起使用）。不幸的是，要使刻度线注释出现在绘图外部，必须使用coord_cartesian(clip = "off")，这意味着绘图区域之外的任何其他内容也会被暴露（参见下面的reprex）。

或者，也许有一种方法可以利用 ggplot2 v3.3.0 的任何新功能来绘制小刻度，而不是作为注释，而是作为轴/绘图的实际部分，以便可以将它们绘制到外部绘图区。

我不是软件开发人员，但也许有人可以使用 register_theme_elements 定义一个名为 axis.minor.ticks 的新主题元素，其行为类似于 axis.ticks，但从 panel_params$y$break_positions_minor 而不是 panel_params$y$break_positions 获取小刻度的适当位置.或者以某种方式使用新的guide_x() S3 函数。

任何帮助将不胜感激！

注解函数和ggproto对象

annotation_ticks() 函数（合并 this fix 用于分面问题）：

annotation_ticks <- function(sides = "b",
                             scale = "identity",
                             scaled = TRUE,
                             ticklength = unit(0.1, "cm"),
                             colour = "black",
                             size = 0.5,
                             linetype = 1,
                             alpha = 1,
                             color = NULL,
                             ticks_per_base = NULL,
                             data = data.frame(x = NA), 
                             ...) {
  if (!is.null(color)) {
    colour <- color
  }

  # check for invalid side
  if (grepl("[^btlr]", sides)) {
    stop(gsub("[btlr]", "", sides), " is not a valid side: b,t,l,r are valid")
  }

  # split sides to character vector
  sides <- strsplit(sides, "")[[1]]

  if (length(sides) != length(scale)) {
    if (length(scale) == 1) {
      scale <- rep(scale, length(sides))
    } else {
      stop("Number of scales does not match the number of sides")
    }
  }

  base <- sapply(scale, function(x) switch(x, "identity" = 10, "log10" = 10, "log" = exp(1)), USE.NAMES = FALSE)

  if (missing(ticks_per_base)) {
    ticks_per_base <- base - 1
  } else {
    if ((length(sides) != length(ticks_per_base))) {
      if (length(ticks_per_base) == 1) {
        ticks_per_base <- rep(ticks_per_base, length(sides))
      } else {
        stop("Number of ticks_per_base does not match the number of sides")
      }
    }
  }

  delog <- scale %in% "identity"

  layer(
    data = data,
    mapping = NULL,
    stat = StatIdentity,
    geom = GeomTicks,
    position = PositionIdentity,
    show.legend = FALSE,
    inherit.aes = FALSE,
    params = list(
      base = base,
      sides = sides,
      scaled = scaled,
      ticklength = ticklength,
      colour = colour,
      size = size,
      linetype = linetype,
      alpha = alpha,
      ticks_per_base = ticks_per_base,
      delog = delog,
      ...
    )
  )
}

ggproto 对象（现在与 ggplot2 v3.3.0 一起使用）：

GeomTicks <- ggproto(
  "GeomTicks", Geom,
  extra_params = "",
  handle_na = function(data, params) {
    data
  },

  draw_panel = function(data,
                        panel_scales,
                        coord,
                        base = c(10, 10),
                        sides = c("b", "l"),
                        scaled = TRUE,
                        ticklength = unit(0.1, "cm"),
                        ticks_per_base = base - 1,
                        delog = c(x = TRUE, y = TRUE)) {
    ticks <- list()

    for (s in 1:length(sides)) {
      if (grepl("[b|t]", sides[s])) {

        # for ggplot2 < 3.3.0 use: xticks <- panel_params$x.minor
        if (utils::packageVersion("ggplot2") >= "3.2.1.9000") {
          x_minor_breaks <- panel_scales$x$break_positions_minor()
          x_major_breaks <- panel_scales$x$break_positions()
        } else {
          x_minor_breaks <- panel_scales$x.minor
          x_major_breaks <- panel_scales$x.major
        }

        xticks <- setdiff(x_minor_breaks, x_major_breaks)

        # Make the grobs
        if (grepl("b", sides[s])) {
          ticks$x_b <- with(
            data,
            segmentsGrob(
              x0 = unit(xticks, "npc"),
              x1 = unit(xticks, "npc"),
              y0 = unit(0, "npc"),
              y1 = ticklength,
              gp = gpar(
                col = alpha(colour, alpha),
                lty = linetype,
                lwd = size * .pt
              )
            )
          )
        }
        if (grepl("t", sides[s])) {
          ticks$x_t <- with(
            data,
            segmentsGrob(
              x0 = unit(xticks, "npc"),
              x1 = unit(xticks, "npc"),
              y0 = unit(1, "npc"),
              y1 = unit(1, "npc") - ticklength,
              gp = gpar(
                col = alpha(colour, alpha),
                lty = linetype,
                lwd = size * .pt
              )
            )
          )
        }
      }


      if (grepl("[l|r]", sides[s])) {

        # for ggplot2 < 3.3.0 use: yticks <- panel_params$y.minor
        if (utils::packageVersion("ggplot2") >= "3.2.1.9000") {
          y_minor_breaks <- panel_scales$y$break_positions_minor()
          y_major_breaks <- panel_scales$y$break_positions()
        } else {
          y_minor_breaks <- panel_scales$y.minor
          y_major_breaks <- panel_scales$y.major
        }

        yticks <- setdiff(y_minor_breaks, y_major_breaks)

        # Make the grobs
        if (grepl("l", sides[s])) {
          ticks$y_l <- with(
            data,
            segmentsGrob(
              y0 = unit(yticks, "npc"),
              y1 = unit(yticks, "npc"),
              x0 = unit(0, "npc"),
              x1 = ticklength,
              gp = gpar(
                col = alpha(colour, alpha),
                lty = linetype, lwd = size * .pt
              )
            )
          )
        }
        if (grepl("r", sides[s])) {
          ticks$y_r <- with(
            data,
            segmentsGrob(
              y0 = unit(yticks, "npc"),
              y1 = unit(yticks, "npc"),
              x0 = unit(1, "npc"),
              x1 = unit(1, "npc") - ticklength,
              gp = gpar(
                col = alpha(colour, alpha),
                lty = linetype,
                lwd = size * .pt
              )
            )
          )
        }
      }
    }
    gTree(children = do.call("gList", ticks))
  },
  default_aes = aes(colour = "black", size = 0.5, linetype = 1, alpha = 1)
)

带有coord_cartesian(clip = "on")的图表

线宽很粗的列看起来不错，但看不到刻度注释。

library(ggplot2)
library(grid)

ggplot(mpg, aes(x = class, y = displ, fill = class)) + 
  stat_summary(fun = mean, geom = "col", colour = "black", size = 1) + 
  theme_classic(base_size = 8) + 
  scale_y_continuous(limits = c(0, 8), expand = c(0, 0)) + 
  annotation_ticks(sides = "l", ticklength = -1 * unit(0.2, "cm")) + 
  coord_cartesian(clip = "on")

ggsave("clip_on.png", device = "png", width = 4, height = 3)

column plot with clip=on

用coord_cartesian(clip = "off") 绘制图表

勾选注释可见，但线宽很粗的列显示在绘图区域之外。

ggplot(mpg, aes(x = class, y = displ, fill = class)) + 
  stat_summary(fun = mean, geom = "col", colour = "black", size = 1) + 
  theme_classic(base_size = 8) + 
  scale_y_continuous(limits = c(0, 8), expand = c(0, 0)) + 
  annotation_ticks(sides = "l", ticklength = -1 * unit(0.2, "cm")) + 
  coord_cartesian(clip = "off")

ggsave("clip_off.png", device = "png", width = 4, height = 3)

column plot with clip=off

Answer 1

这段代码对我来说似乎很熟悉，所以我想权衡一下。

是的，随着 ggplot v3.3.0 指南变得可扩展，虽然我怀疑它们会在很长一段时间内保持当前形式，因为通过小道消息，我听说他们也想将指南切换到 ggproto 系统。

没有太多花里胡哨的最便宜的方法就是调整向导的向导培训部分。由于这是一个 S3 方法，我们需要一个新的指导类来编写自定义方法：

library(ggplot2)
library(rlang)
#> Warning: package 'rlang' was built under R version 3.6.3
library(glue)

guide_axis_minor <- function(
  title = waiver(), check.overlap = FALSE, angle = NULL,
  n.dodge = 1, order = 0, position = waiver()
) {
  structure(list(title = title, check.overlap = check.overlap, 
                 angle = angle, n.dodge = n.dodge, order = order, position = position, 
                 available_aes = c("x", "y"), name = "axis"), 
            class = c("guide", "axis_minor", "axis"))
}

您会注意到，上面的函数与guide_axis() 相同，只是多了一个类。在这里类的顺序很重要，因为我们继承了axis 类，这样我们就可以偷懒，只使用所有已经存在的方法。

这给我们带来了训练，确实是唯一需要稍微调整的东西。我已经在相关部分发表了评论。大部分功能仍与guide_train.axis 内部功能相同。简而言之，我们将次要中断视为带有空标签的重大中断。

guide_train.axis_minor <- function(guide, scale, aesthetic = NULL) {
  aesthetic <- aesthetic %||% scale$aesthetics[1]

  # Seperately define major and minor breaks
  major_breaks <- scale$get_breaks()
  minor_breaks <- scale$get_breaks_minor()

  # We set the actual breaks to be both major and minor
  breaks <- union(major_breaks, minor_breaks)

  # We keep track of what breaks were the major breaks
  is_major <- breaks %in% major_breaks

  empty_ticks <- ggplot2:::new_data_frame(
    list(aesthetic = numeric(), .value = numeric(0), .label = character())
  )
  if (length(intersect(scale$aesthetics, guide$available_aes)) == 0) {
    warn(glue("axis guide needs appropriate scales: ", 
              glue_collapse(guide$available_aes, ", ", last = " or ")))
    guide$key <- empty_ticks
  } else if (length(breaks) == 0) {
    guide$key <- empty_ticks
  } else {
    mapped_breaks <- if (scale$is_discrete()) {
      scale$map(breaks)
    } else {
      breaks
    }
    ticks <- ggplot2:::new_data_frame(setNames(list(mapped_breaks), 
                                     aesthetic))
    ticks$.value <- breaks
    ticks$.label <- scale$get_labels(breaks)

    # Now this is the bit where we set minor breaks to have empty labls
    ticks$.label[!is_major] <- ""

    guide$key <- ticks[is.finite(ticks[[aesthetic]]), ]
  }
  guide$name <- paste0(guide$name, "_", aesthetic)
  guide$hash <- digest::digest(list(guide$title, guide$key$.value, 
                                    guide$key$.label, guide$name))
  guide
}

然后，因为我们继承了axis 类，为该类编写的所有函数也适用于我们的axis_minor 类，所以我们完成了。现在您可以通过名称从任何连续位置标度调用指南：

ggplot(mpg, aes(x = class, y = displ, fill = class)) + 
  stat_summary(fun = mean, geom = "col") + 
  scale_y_continuous(limits = c(0, 8), 
                     guide = "axis_minor")

^{由reprex package (v0.3.0) 于 2020-04-07 创建}