如何协调facet_wrap和scale =“ free_y”内的轴？

Question

我想画出连续变量和分类变量（geom_boxplot和ggplot2）之间的关系的箱线图，这适用于几种情况（facet_wrap）。很简单：

data("CO2")
ggplot(CO2, aes(Treatment, uptake) ) + 
  geom_boxplot(aes(Treatment, uptake), 
               col="black", fill="white", alpha=0, width=.5) + 
  geom_point(col="black", size=1.2) + 
  facet_wrap(~Type, ncol=3, nrow=6, scales= "free_y") + 
  theme_bw() + 
  ylab("Uptake")

结果：

这个玩具数据集非常不错，但是应用于我自己的数据（其中facet_wrap使我可以绘制18个不同的图）y轴几乎不可读，其y标记的数量和间距都不同：

什么是协调y轴的好方法？ （即，无论中断是什么，在y轴刻度线之间获取相等的间距-由于连续变量的变化范围变化很​​大，因此这些位置必定会从一个图变为另一个图）

非常感谢您的帮助：）

Answer 1

通过在y轴值上应用pretty()并扩展第一个值/最后一个值，可以手动扩展每个构面的值，从而将每个构面的限制强制为相对漂亮的外观。

以下是使用钻石数据集的示例：

# normal facet_wrap plot with many different y-axis scales across facets
p <- ggplot(diamonds %>% filter(cut %in% c("Fair", "Ideal")), 
       aes(x = cut, y = carat) ) + 
  geom_boxplot(col="black", fill="white", alpha=0, width=.5) + 
  geom_point(col="black", size=1.2) + 
  facet_wrap(~clarity, scales= "free_y", nrow = 2) + 
  theme_bw() + 
  ylab("Uptake")

p

# modified plot with consistent label placements
p + 
  # Manually create values to expand the scale, by finding "pretty" 
  # values that are slightly larger than the range of y-axis values 
  # within each facet; set alpha = 0 since they aren't meant to be seen
  geom_point(data = . %>% 
               group_by(clarity) %>% #group by facet variable
               summarise(y.min = pretty(carat)[1],
                         y.max = pretty(carat)[length(pretty(carat))]) %>%
               tidyr::gather(key, value, -clarity), 
             aes(x = 1, y = value),
             inherit.aes = FALSE, alpha = 0) +

  # Turn off automatical scale expansion, & manually set scale breaks
  # as an evenly spaced sequence (with the "pretty" values created above
  # providing the limits for each facet). If there are many facets to
  # show, I recommend no more than 3 labels in each facet, to keep things
  # simple.
  scale_y_continuous(breaks = function(x) seq(from = x[1], 
                                              to = x[2], 
                                              length.out = 3), 
                     expand = c(0, 0))

Answer 2

只需将scales= "free_y"内的geom_point移开，即可得到所需的东西。

但是，MrFlick在评论中正确地指出了这一点，即使间距也绝对会导致轴上出现疯狂的怪异数字