如何在R的ggplot循环生成的柱状图中添加非NA观测总数

我正在处理包含250列的调查数据，数据示例如下：

q1 <- factor(c("yes","yes","no","yes",NA,"yes","no","yes"))
q2 <- factor(c("Albania","USA","Albania","Albania","UK",NA,"UK","Albania"))
q3 <- factor(c(0,1,0,0,1,1,0,0))
q4 <- factor(c(0,NA,NA,NA,1,NA,0,0))
q5 <- factor(c("Dont know","Prefer not to answer","Agree","Disagree",NA,"Agree","Agree",NA))
q6 <- factor(c(1,NA,3,5,800,NA,900,2))

data <- data.frame(q1,q2,q3,q4,q5,q6)

为了循环遍历所有列并生成答案分布的柱状图列表，我用了以下代码：

barplot_list <- lapply(names(data), function(variable) {
  ggplot(
    data = data,
    mapping = aes(.data[[variable]])
  ) +
    geom_bar(width = 0.6, fill = "#0096FF") +
    labs(x = variable, y = "response count") +
    geom_text(aes(label=..count..),stat='count',position=position_dodge(0.9),hjust=-0.1)+
    scale_fill_brewer(palette = "Set2") +
    theme_bw() +
    theme(panel.grid.major.y = element_blank()) +
    coord_flip()
})

现在想为每个柱状图添加排除NA值后的观测总数，可显示在图例、图表内或标题处。我尝试过geom_text(stat = "count",aes(label = after_stat(sum(count))))，但会在每个柱子顶部显示总数。请问如何修改代码，使每个图中显示“Total = N”（N为对应列排除NA后的观测总数）？

解决方案1：将总数添加到图表标题中 #

在循环内部先计算当前列的非NA观测数，再把总数拼接进标题文本，修改后的代码如下：

barplot_list <- lapply(names(data), function(variable) {
  # 计算当前列非NA的观测总数
  total_obs <- sum(!is.na(data[[variable]]))
  ggplot(
    data = data,
    mapping = aes(.data[[variable]])
  ) +
    geom_bar(width = 0.6, fill = "#0096FF") +
    labs(
      x = variable, 
      y = "response count",
      title = paste0(variable, " - Total = ", total_obs)  # 标题中嵌入总数
    ) +
    geom_text(aes(label=after_stat(count)), stat='count', position=position_dodge(0.9), hjust=-0.1)+
    scale_fill_brewer(palette = "Set2") +
    theme_bw() +
    theme(panel.grid.major.y = element_blank()) +
    coord_flip()
})

解决方案2：在图表角落添加总数文本 #

如果不想修改标题，可使用annotate()在图表固定位置（比如右上角）添加总数文本，代码如下：

barplot_list <- lapply(names(data), function(variable) {
  total_obs <- sum(!is.na(data[[variable]]))
  ggplot(
    data = data,
    mapping = aes(.data[[variable]])
  ) +
    geom_bar(width = 0.6, fill = "#0096FF") +
    labs(x = variable, y = "response count") +
    geom_text(aes(label=after_stat(count)), stat='count', position=position_dodge(0.9), hjust=-0.1)+
    # 在右上角添加总数文本
    annotate("text", x = Inf, y = Inf, label = paste0("Total = ", total_obs), 
             hjust = 1.1, vjust = 1.1, size = 4, color = "darkgray") +
    scale_fill_brewer(palette = "Set2") +
    theme_bw() +
    theme(panel.grid.major.y = element_blank()) +
    coord_flip()
})

关键说明： #

• 两种方法都是先在循环内计算total_obs <- sum(!is.na(data[[variable]]))，确保每个图表获取对应列的非NA总数。
• 把原代码中的..count..替换为after_stat(count)，这是ggplot2 3.0+版本推荐的标准语法，兼容性更强。

内容的提问来源于stack exchange，提问作者dryl