如何在geom_density_ridges2()中去除NA水平并保留x轴刻度

背景 #

为了让x轴显示0、1、2这些原本缺失的刻度值，我尝试用complete(value = seq(0, max(value), 1))为数据框的value列补充缺失值行，但生成的图中出现了NA的y轴水平（如下左图），期望得到没有NA水平且保留x轴0-9完整刻度的图（如下右图）：

解决方案 #

问题根源在于complete函数未按item分组补全数据，导致生成了没有对应item的行（即item为NA的行）。只需修改complete的参数，按item分组来补全每个item对应的所有value值即可：

将complete(value = seq(0, max(value), 1))改为complete(item, value = seq(0, max(value), 1))

修改后的完整代码 #

library(dplyr)
library(tidyr)
library(ggplot2)
library(ggridges)

df %>%
  # 按item分组补全每个item对应的所有value值
  complete(item, value = seq(0, max(value), 1)) %>%
  ggplot(aes(x = value, y = item, group = item)) +
  geom_density_ridges2(aes(fill = item), 
                       stat = "binline", 
                       binwidth = 1, 
                       scale = 0.95) +
  geom_text(
    stat = "bin",
    aes(
      y = group + 0.95*stat(count/max(count)),
      label = ifelse(stat(count) > 0, stat(count), "")
    ),
    vjust = -0.5, size = 3, color = "black", binwidth = 1
  ) +
  scale_x_continuous(
    breaks = 0:9, 
    name = "Answer (higher = better)"
  ) +
  scale_y_discrete(
    expand = expansion(add = 2)
  ) +
  scale_fill_viridis_d() +
  labs(
    title = "Example",
    y = NULL
  ) +
  theme_ridges(grid = FALSE) +
  theme(
    axis.title.x = element_text(hjust = 0.5),
    axis.title.y = element_text(hjust = 0.5),
    legend.position = "none",
    plot.title.position = "plot",
    plot.title = element_text(face="bold")
  )

数据 #

df <- structure(list(id = c(1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 
7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 
16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 23, 
24, 24, 25, 25, 26, 26, 27, 27, 28, 28, 29, 29), item = structure(c(1L, 
2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 
2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 
2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 
2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L), .Label = c("A", "B", "C", 
"D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N"), class = "factor"), 
    value = c(8, 9, 4, 5, 8, 9, 7, 9, 8, 8, 7, 6, 9, 8, 9, 9, 
    9, 9, 8, 9, 9, 9, 8, 9, 8, 8, 7, 8, 8, 8, 7, 9, 8, 9, 8, 
    9, 9, 9, 9, 9, 8, 9, 9, 9, 9, 7, 9, 9, 8, 9, 8, 9, 7, 9, 
    7, 7, 7, 8)), row.names = c(NA, -58L), class = c("tbl_df", 
"tbl", "data.frame"))

内容的提问来源于stack exchange，提问作者TarJae