r - 如何使用 forcats 根据另一个变量的子集(方面)重新排序一个因子？

Question

forcats vignette指出

The goal of the forcats package is to provide a suite of useful tools that solve common problems with factors

事实上，其中一个工具是通过另一个变量对因子重新排序，这是绘制数据时非常常见的用例。我试图使用 forcats 来完成这个，但在多面情节的情况下。也就是说，我想通过其他变量重新排序一个因子，但只使用数据的一个子集。这是一个代表:

library(tidyverse)

ggplot2::diamonds %>% 
    group_by(cut, clarity) %>% 
    summarise(value = mean(table, na.rm = TRUE)) %>%
    ggplot(aes(x = clarity, y = value, color = clarity)) + 
    geom_segment(aes(xend = clarity, y = min(value), yend = value), 
                 size = 1.5, alpha = 0.5) + 
    geom_point(size = 3) + 
    facet_grid(rows = "cut", scales = "free") +
    coord_flip() +
    theme(legend.position = "none")

这段代码生成的情节接近我想要的:

但我希望净度轴按值排序，这样我可以快速找出哪个净度值最高。但是每个方面都意味着不同的顺序。所以我想选择按特定方面内的值对绘图进行排序。

forcats 的直接使用当然在这种情况下不起作用，因为它会根据所有值而不只是特定方面的值对因子重新排序。让我们开始吧:

# Inserting this line right before the ggplot call
mutate(clarity = forcats::fct_reorder(clarity, value)) %>%

然后生成此图。

当然，它根据整个数据对因子进行了重新排序，但是如果我希望绘图按“理想”切割的值排序怎么办？如何使用 forcats 执行此操作？

我目前的解决方案如下:

ggdf <- ggplot2::diamonds %>% 
    group_by(cut, clarity) %>% 
    summarise(value = mean(table, na.rm = TRUE))

# The trick would be to create an auxiliary factor using only
# the subset of the data I want, and then use the levels
# to reorder the factor in the entire dataset.
#
# Note that I use good-old reorder, and not the forcats version
# which I could have, but better this way to emphasize that
# so far I haven't found the advantage of using forcats 
reordered_factor <- reorder(ggdf$clarity[ggdf$cut == "Ideal"], 
                            ggdf$value[ggdf$cut == "Ideal"])

ggdf$clarity <- factor(ggdf$clarity, levels = levels(reordered_factor))

ggdf %>%
    ggplot(aes(x = clarity, y = value, color = clarity)) + 
    geom_segment(aes(xend = clarity, y = min(value), yend = value), 
                 size = 1.5, alpha = 0.5) + 
    geom_point(size = 3) + 
    facet_grid(rows = "cut", scales = "free") +
    coord_flip() +
    theme(legend.position = "none")

产生我想要的东西。

但我想知道使用 forcats 是否有更优雅/更聪明的方法。

Answer 1

如果你想根据特定方面的值重新排序 clarity，你必须告诉 forcats::fct_reorder() 这样做，例如，

mutate(clarity = forcats::fct_reorder(
    clarity, filter(., cut == "Ideal") %>% pull(value)))

它仅使用“理想”方面的值进行重新排序。

因此，

ggplot2::diamonds %>% 
  group_by(cut, clarity) %>% 
  summarise(value = mean(table, na.rm = TRUE)) %>%
  mutate(clarity = forcats::fct_reorder(
    clarity, filter(., cut == "Ideal") %>% pull(value))) %>%
  ggplot(aes(x = clarity, y = value, color = clarity)) + 
  geom_segment(aes(xend = clarity, y = min(value), yend = value), 
               size = 1.5, alpha = 0.5) + 
  geom_point(size = 3) + 
  facet_grid(rows = "cut", scales = "free") +
  coord_flip() +
  theme(legend.position = "none")

创造

根据要求。