如何将R ggplot2中geom_bar的颜色统一设置为#0277BD？

我尝试把柱状图所有柱子的颜色统一设为#0277BD，用scale_fill_manual(values=c("#0277BD"))时出现错误：

Error in `f()`:
! Insufficient values in manual scale. 24 needed but only 1 provided.

改用scale_fill_brewer(palette="Blues")又得到警告：

Warning message:
In RColorBrewer::brewer.pal(n, pal) :
  n too large, allowed maximum for palette Blues is 9
Returning the palette you asked for with that many colors

数据 #

df = structure(list(CITYNAME = c("a", "b", "c", 
    "d", "e", "f", "g", 
    "h", "i", "j", "k", 
    "l", "m", "n", "p", "q", 
    "r", "s", "t", "u", 
    "w", "x", "y", "z"), AvgTMin = c(20.28, 
20.38, 20.08, 20.35, 20.38, 20.76, 21, 21.21, 20.45, 20.21, 21.18, 
20.29, 20.61, 20.44, 20.95, 19.75, 20.58, 20.32, 21.05, 20.28, 
20.09, 20.15, 20.73, 20.12)), row.names = c(NA, 
    -24L), class = c("tbl_df", "tbl", "data.frame"))

当前代码 #

# 转换为华氏度绘图

df %>% mutate(AvgTMin = AvgTMin * (1.8) + 32) %>% # 从摄氏度转华氏度
      ggplot(aes(x = reorder(CITYNAME,AvgTMin), y = AvgTMin, fill = CITYNAME)) +
      geom_bar(stat="identity") +
      coord_cartesian(ylim = c(60,70.3)) +
      theme(axis.text = element_text(size = 14)) +
      geom_text(aes(label=sprintf("%0.2f", AvgTMin)), vjust=-0.2, size = 4) +
      labs(x = NULL, y = "平均最低温度 °F") + 
      theme(axis.text.x = element_text(angle = 90),  legend.position = 'none') +
      ggtitle("1980-2021 各城市温度趋势")

问题核心是你在aes里把fill映射到了CITYNAME，ggplot会默认给每个不同城市分配独立颜色。要统一颜色，有两种简单方法：

方法1：移除fill映射，直接在geom_bar中设置颜色 #

删掉aes里的fill = CITYNAME，在geom_bar中直接指定填充色，这是最直接的方式：

df %>% mutate(AvgTMin = AvgTMin * (1.8) + 32) %>%
      ggplot(aes(x = reorder(CITYNAME,AvgTMin), y = AvgTMin)) +
      geom_bar(stat="identity", fill = "#0277BD") + # 直接设置统一填充色
      coord_cartesian(ylim = c(60,70.3)) +
      theme(axis.text = element_text(size = 14)) +
      geom_text(aes(label=sprintf("%0.2f", AvgTMin)), vjust=-0.2, size = 4) +
      labs(x = NULL, y = "平均最低温度 °F") + 
      theme(axis.text.x = element_text(angle = 90),  legend.position = 'none') +
      ggtitle("1980-2021 各城市温度趋势")

方法2：保留fill映射，重复单一颜色匹配类别数量 #

如果需要保留fill的映射（比如后续有扩展需求），可以用rep()函数让scale_fill_manual为所有城市重复同一个颜色：

df %>% mutate(AvgTMin = AvgTMin * (1.8) + 32) %>%
      ggplot(aes(x = reorder(CITYNAME,AvgTMin), y = AvgTMin, fill = CITYNAME)) +
      geom_bar(stat="identity") +
      coord_cartesian(ylim = c(60,70.3)) +
      theme(axis.text = element_text(size = 14)) +
      geom_text(aes(label=sprintf("%0.2f", AvgTMin)), vjust=-0.2, size = 4) +
      labs(x = NULL, y = "平均最低温度 °F") + 
      theme(axis.text.x = element_text(angle = 90),  legend.position = 'none') +
      ggtitle("1980-2021 各城市温度趋势") +
      scale_fill_manual(values = rep("#0277BD", nrow(df))) # 重复颜色匹配城市数量

内容的提问来源于stack exchange，提问作者Ed_Gravy