扩展ggplot2 Geom以更改x和y轴的默认“填充”

Question

引用Extending ggplot2指南，假设我想创建自己的geom，其中默认的ggplot行为是：

• x轴完全从min(x)到max(x)
• y轴完全从min(y)到max(y)

没有填充！ （比如所有geoms的当前默认行为）

让我们重复指南中的例子，geom_simple_point：

GeomSimplePoint <- ggproto("GeomSimplePoint", Geom,
  required_aes = c("x", "y"),
  default_aes = aes(shape = 19, colour = "black"),
  draw_key = draw_key_point,

  draw_panel = function(data, panel_params, coord) {
    coords <- coord$transform(data, panel_params)
    grid::pointsGrob(
      coords$x, coords$y,
      pch = coords$shape,
      gp = grid::gpar(col = coords$colour)
    )
  }
)

geom_simple_point <- function(mapping = NULL, data = NULL, stat = "identity",
                              position = "identity", na.rm = FALSE, show.legend = NA, 
                              inherit.aes = TRUE, ...) {
  layer(
    geom = GeomSimplePoint, mapping = mapping,  data = data, stat = stat, 
    position = position, show.legend = show.legend, inherit.aes = inherit.aes,
    params = list(na.rm = na.rm, ...)
  )
}

ggplot(mpg, aes(displ, hwy)) + 
  geom_simple_point()

在哪里可以更改代码以使面板默认延伸到数据（min到max，x和y，没有填充）？即只有红色虚线中的内容：

我看着draw_key，似乎没有关系。我看着draw_panel，似乎没有参与照顾它。

更新：如果我在print(panel_params)中添加draw_panel，我可以看到这是ggplot获得填充或扩展的“想法”的地方：

$x.range
[1] 1.33 7.27

$x.labels
[1] "2" "3" "4" "5" "6" "7"

$x.major
[1] 0.1127946 0.2811448 0.4494949 0.6178451 0.7861953 0.9545455

$x.minor
 [1] 0.02861953 0.11279461 0.19696970 0.28114478 0.36531987 0.44949495 0.53367003 0.61784512 0.70202020 0.78619529
[11] 0.87037037 0.95454545

$x.major_source
[1] 2 3 4 5 6 7

$x.minor_source
 [1] 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

$x.arrange
[1] "secondary" "primary"  

$y.range
[1] 10.4 45.6

$y.labels
[1] "20" "30" "40"

$y.major
[1] 0.2727273 0.5568182 0.8409091

$y.minor
[1] 0.1306818 0.2727273 0.4147727 0.5568182 0.6988636 0.8409091 0.9829545

$y.major_source
[1] 20 30 40

$y.minor_source
[1] 15 20 25 30 35 40 45

$y.arrange
[1] "primary"   "secondary"

如果我手动更改panel_params的x.range和y.range字段，它似乎首先起作用：

GeomSimplePoint <- ggproto("GeomSimplePoint", Geom,
                           required_aes = c("x", "y"),
                           default_aes = aes(shape = 19, colour = "black"),
                           draw_key = draw_key_point,

                           draw_panel = function(data, panel_params, coord) {
                             panel_params$x.range <- range(data$x)
                             panel_params$y.range <- range(data$y)
                             coords <- coord$transform(data, panel_params)
                             grid::pointsGrob(
                               coords$x, coords$y,
                               pch = coords$shape,
                               gp = grid::gpar(col = coords$colour)
                             )
                           }
)

但是如果仔细观察一下情节，你会发现标签及其位置没有改变 - 因为我没有改变它们，我也需要手动完成。

如果我没有选择，我会去手动。但是，有没有办法用一个简单的panel_params参数手动获得expand = FALSE？我查看了ggplot代码，很难找到。

Answer 1

也许你（和我）过度思考。 ... + coord_cartesian(expand = FALSE)给出你想要的输出。并且如How can I combine multiple ggplot2 elements into the return of a function?所述，您可以使用+ coord_cartesian()将list()组合到您的函数中。

我想这就是你想要的;

geom_simple_point2 <- function(mapping = NULL, data = NULL, stat = "identity",
                               position = "identity", na.rm = FALSE, show.legend = NA, 
                               inherit.aes = TRUE, ...) {
  list(
    layer(
      geom = GeomSimplePoint, mapping = mapping,  data = data, stat = stat, 
      position = position, show.legend = show.legend, inherit.aes = inherit.aes,
      params = list(na.rm = na.rm, ...)
    ),
    coord_cartesian(expand = FALSE)
  )
}