操作ggproto以获得多个层

Question

我试图从ggproto对象中获取多个区域层。我不知道这是否可能，但如果是的话，我不知道怎么做。

例如，如何让下面的代码生成两个区域层，其中一个有y坐标作为另一个区域的一半-

StatDensityHalf <- ggproto("StatDensity2", Stat, 
  required_aes = "x",
  default_aes = aes(y = ..density..),

  compute_group = function(data, scales, bandwidth = 1) {
    d <- density(data$x, bw = bandwidth)
    rbind(
       data.frame(x = d$x, density = d$y, fill = 1),
       data.frame(x = d$x, density = d$y/2, fill =2)
    )
  }  
)

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


ggplot(mpg, aes(displ)) + 
  stat_density_half(bandwidth = 1, geom = "area", position = "stack")

请注意，我并不是在寻找解决办法来产生与示例所建议的相同的情节。我正在寻找这个问题的通用解决方案。

Answer 1

好吧，终于有时间完成这件事了。这就创建了两个层：

library(ggplot2)

StatDensityHalf <- 
    ggproto("StatDensity2", Stat,
            required_aes = "x",
            default_aes = aes(y = ..density..),
            compute_group = function(data, scales, bandwidth = 1,fak=1,fillgrp="1"){
                 d <- density(data$x, bw = bandwidth)
                data.frame(x = d$x, density = d$y / fak, fill = fillgrp)
             }
    )

stat_density_half <- function(mapping = NULL, data = NULL, geom = "line", 
                              position = "identity", na.rm = FALSE, show.legend = NA,
                              inherit.aes = TRUE, bandwidth = NULL, ...) {
    list(
      layer(
        stat = StatDensityHalf, data = data, mapping = mapping, geom = geom,
        position = position, show.legend = show.legend, inherit.aes = inherit.aes,
        params = list(bandwidth = bandwidth, na.rm = na.rm, fak = 1, fillgrp = "1", ...)),

      layer(
        stat = StatDensityHalf, data = data, mapping = mapping, geom = geom,
        position = position, show.legend = show.legend, inherit.aes = inherit.aes,
        params = list(bandwidth = bandwidth, na.rm = na.rm, fak = 2, fillgrp = "2", ...))
      )
    }

ggplot(mpg, aes(cty)) +
  stat_density_half(bandwidth = 2, geom = "area", position = "stack") +
  scale_fill_manual(values = c("2" = "red", "1" = "blue"))

产量：

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更新：

在第一次迭代中，我有两个ggproto，因为我没有真正了解如何将参数添加到ggproto (这里是fak和fillgrp)，解决方案是将它们显式地添加到compute_group函数中，并将它们添加到params列表中，否则ggproto包装器会出现故障。