ggplot2设置图例背景圆角遇‘unused argument’错误的解决问询

错误原因 #

你遇到的报错是因为ggplot2原生的element_rect()函数根本没有radius参数，不管传unit(0.1, "snpc")还是0.1都会被识别为无效参数，所以触发"unused argument"错误。

两种可行解决方案 #

方案1：用ggtext包的圆角矩形元素（推荐） #

ggtext包提供了支持圆角的element_rect_round()函数，用法和element_rect()几乎一致，只是多了radius参数。

修改后的完整代码：

library(tidyverse)
library(ggplot2)
library(ggthemes)
library(grid)
library(ggtext) # 新增加载ggtext包

read.csv("/Users/benjamincohn/Desktop/R studio/vaccination_percentages.csv") -> un

un %>%
  arrange(Uninsured) %>%
  ggplot(aes(y = Life.Expectancy.at.Birth..years., x = Uninsured, color = Location)) +
  geom_point() +
  scale_x_continuous(breaks = seq(2, 18, by = 1)) +
  scale_y_continuous(breaks = seq(70, 81, by = 1)) +
  geom_smooth(method = "lm", color = 'black') +
  ggtitle("Uninsured (%) vs. Life Expectancy at Birth (years) by State (2023)") +
  labs(y = "Life Expectancy at Birth (years)", x = "Uninsured (%)") +
  theme(axis.line = element_line(colour = "black", size = 1, linetype = "solid"),
        plot.background = element_rect_round(fill = "lightblue", radius = unit(0.1, "snpc")), # 替换为支持圆角的元素
        legend.key = element_rect(fill = "deepskyblue3"),
        legend.background = element_rect_round(fill = "deepskyblue3", radius = unit(0.1, "snpc"))) # 替换为支持圆角的元素

方案2：用grid包自定义圆角元素（无需额外装包） #

如果不想新增依赖，可以用grid包的roundrectGrob()创建圆角矩形，再通过annotation_custom()添加到图表中，适合需要精细控制位置的场景：

示例（以图例背景为例）：

# 先绘制基础图表
p <- un %>%
  arrange(Uninsured) %>%
  ggplot(aes(y = Life.Expectancy.at.Birth..years., x = Uninsured, color = Location)) +
  geom_point() +
  scale_x_continuous(breaks = seq(2, 18, by = 1)) +
  scale_y_continuous(breaks = seq(70, 81, by = 1)) +
  geom_smooth(method = "lm", color = 'black') +
  ggtitle("Uninsured (%) vs. Life Expectancy at Birth (years) by State (2023)") +
  labs(y = "Life Expectancy at Birth (years)", x = "Uninsured (%)") +
  theme(axis.line = element_line(colour = "black", size = 1, linetype = "solid"),
        plot.background = element_rect(fill = "lightblue"),
        legend.key = element_rect(fill = "deepskyblue3"),
        legend.background = element_blank()) # 先清空默认图例背景

# 添加自定义圆角图例背景
library(grid)
round_legend_bg <- roundrectGrob(x = 0, y = 1, width = 1, height = 1,
                                 r = unit(0.1, "snpc"), fill = "deepskyblue3",
                                 just = c("left", "top"))
p + annotation_custom(round_legend_bg, xmin = Inf, xmax = Inf, ymin = -Inf, ymax = Inf)

内容的提问来源于stack exchange，提问作者lubalubadubdub