如何调整R语言barplot的图例框大小及位置？

方法1：调整args.legend参数实现缩小+移动 #

直接在args.legend里补充缩放、边框和偏移参数，就能解决遮挡问题：

score <- tapply(exams$writing.score 
               , list(exams$gender,
                      exams$race.ethnicity
                      )
               , mean)

plot1 <- barplot(score
                 , beside = TRUE
                 , main = "Comparison of Writing Score"
                 , col = c("red", "lightyellow")
                 , xlab = "Race Ethnicity Group"
                 , ylab = "Average Writing Score"
                 , legend.text = c("Female", "Male")
                 , args.legend = list(x = "topright", cex = 0.8, bty = "n", inset = c(0.02, 0.02))
)

• cex = 0.8：把图例文本和符号缩小到原来的80%
• bty = "n"：去掉图例边框，减少视觉遮挡
• inset = c(0.02, 0.02)：让图例往绘图区域内偏移一点，避免贴边同时远离柱状条

方法2：单独调用legend()函数（更灵活） #

如果自带的图例参数不好控制，直接去掉legend.text，手动添加图例：

score <- tapply(exams$writing.score 
               , list(exams$gender,
                      exams$race.ethnicity
                      )
               , mean)

# 先绘制柱状图，不附带图例
plot1 <- barplot(score
                 , beside = TRUE
                 , main = "Comparison of Writing Score"
                 , col = c("red", "lightyellow")
                 , xlab = "Race Ethnicity Group"
                 , ylab = "Average Writing Score"
)

# 手动添加图例
legend("topright", 
       legend = c("Female", "Male"), 
       fill = c("red", "lightyellow"), 
       cex = 0.8, 
       bty = "n", 
       inset = c(0.02, 0.02))

这种方式可以精准控制所有图例属性，要是还是遮挡，还能调整inset数值，或者把位置改成topleft/bottomright，甚至用具体坐标（比如x = max(plot1) + 1, y = max(score)）来定位。

内容的提问来源于stack exchange，提问作者Tye N