R语言使用基础barplot函数修改柱状图X轴文本格式的方案问询

你需要的分上下两层的X轴样式（下层标注旬标记、上层居中标注月份）可通过基础绘图的axis()与边距设置实现，无需引入ggplot体系。以下是基于你的代码修改后的可运行版本：

# 加载原始数据
df <- data.frame(DK= c("08-01","08-11","08-21","09-01","09-11","09-21","10-01","10-11","10-21","11-01","11-11","11-21","12-01","12-11","12-21","01-01","01-11","01-21","02-01","02-11","02-21","03-01","03-11","03-21","04-01","04-11","04-21","05-01","05-11","05-21","06-01","06-11","06-21","07-01","07-11","07-21"), 
                 value=c(3.9,4.4,5.1,7.1,6.1,7.0,7.8,11.3,13.5,19.6,24.9,27.5,28.0,28.6,41.0,34.3,45.1,43.7,36.0,41.6,27.2,34.3,18.6,24.0,14.0,13.7,12.3,8.5,7.4,6.5,6.2,5.2,5.9,6.3,6.2,7.1))

toplot <- df
# 调整底边绘图边距，给两层X轴留出足够显示空间
par(mar = c(6, 4, 2, 2), repr.plot.width=6, repr.plot.height=4) 
maxv <- max(toplot[,2])+10

# 拆分两层标签：下层是每个柱子对应的旬标签，上层是月份标签
sub_labels <- rep(c("d1","d2","d3"), 12)
# 月份顺序和数据中的日期保持一致：从8月到次年7月
month_labels <- c("Aug","Sep","Oct","Nov","Dec","Jan","Feb","Mar","Apr","May","Jun","Jul")

# 绘制柱状图，关闭默认X轴输出
a <- barplot(toplot$value, 
            col='deepskyblue3', 
            xaxt = "n", yaxt = "n", 
            ylim=c(0,maxv),
            cex.lab=0.75
) 

# 绘制第一层X轴：对应每个柱子的旬标签
axis(1, cex.axis=0.55, las=2, at=a, labels=sub_labels, line = 0) 

# 计算月份标签的居中位置：取每个月3个柱子X坐标的平均值
month_pos <- tapply(a, rep(1:12, each=3), mean)
# 绘制第二层X轴：居中显示的月份标签，通过line参数调整到下层标签上方
axis(1, at = month_pos, labels = month_labels, cex.axis = 0.7, line = 2, tick = TRUE, las = 1)

# 绘制Y轴
axis(2, las=2, cex.axis=0.6)

核心实现逻辑 #

• 提前拆分两层标签，避免原始的月份+旬组合标签拥挤重叠
• 通过line参数控制两层X轴的上下偏移量，保证显示不重叠
• 对每个月3个柱子的X坐标取均值，确保上层月份标签刚好在对应月份柱组的居中位置
• 提前调整par(mar)参数扩大底边边距，避免标签被画布截断

内容的提问来源于stack exchange，提问作者gianca