如何阻止R语言自动按字母排序？修正月度柱状图月份顺序

嘿，这个问题太常见了！你的图表里月份按字母排列，是因为Month列目前是字符类型，ggplot默认会按照字符的字母顺序来排序。咱们只需要把它转换成有序因子，指定好自然月份的顺序，就能解决这个问题啦。

具体修正步骤： #

核心思路是给Month列设置明确的顺序规则，让ggplot知道该按什么顺序展示。你可以选以下两种方式处理：

方法1：创建数据框时直接指定有序因子

Number <- c(41,23,22,16,21,10,10,13,20,12,15,16,18,20,18,92,81,72,73,47,57,12,23,12,12,23,34,54,32,5,65,44,55,66,55,44)
Year <- c("2018","2018","2018","2018","2018","2018","2018","2018","2018","2018","2018","2018","2019","2019","2019","2019","2019","2019","2019","2019","2019","2019","2019","2019","2020","2020","2020","2020","2020","2020","2020","2020","2020","2020","2020","2020")
Month <- c("Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec","Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec","Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec")
library(ggplot2)

# 创建数据框时，把Month转换成有序因子，指定自然月份顺序
adultmonthly <- data.frame(
  Number,
  Year,
  Month = factor(Month,
                 levels = c("Jan","Feb","Mar","Apr","May","Jun",
                            "Jul","Aug","Sep","Oct","Nov","Dec"),
                 ordered = TRUE)
)

# 绘制图表，现在月份会按自然顺序排列
ggplot(adultmonthly, aes(Year, Number, fill = Month)) +
  geom_bar(colour = "black", stat="identity", position = "dodge") +
  labs(title="Frequency of children affected")

方法2：已创建数据框后修改

如果你已经有了adultmonthly数据框，只需要添加这一行代码再绘图：

# 重新定义Month为有序因子
adultmonthly$Month <- factor(adultmonthly$Month,
                            levels = c("Jan","Feb","Mar","Apr","May","Jun",
                                       "Jul","Aug","Sep","Oct","Nov","Dec"),
                            ordered = TRUE)

为什么这样有效？ #

在R中，**因子（factor）**类型的变量会存储类别和对应的顺序规则。当你指定levels参数时，就告诉了R这些月份的正确顺序；ordered=TRUE则标记这是一个有序因子，ggplot会遵循这个顺序来展示图例和分组，而不是默认的字母排序。

内容的提问来源于stack exchange，提问作者Megan D