如何调整ggplot2图例中线条的粗细？

问题分析 #

你遇到的核心问题是：通过guide_legend(override.aes = list(size = 15))设置图例线条加粗时，要么无效果，要么图例整体放大但线条区分度仍不足。这是因为设置的size数值过大，导致图例的key区域被过度撑开，视觉上掩盖了线条加粗的效果；同时geom_line的aes中同时绑定了color和size因子映射，需要精准覆盖参数。另外你的代码存在语法错误：temp %>应改为temp %>%，否则无法正常运行。

修正后的代码 #

library(ggplot2)
library(dplyr)
library(countrycode)

set.seed(123)

temp <- data.frame(
  Year = rep(1995:2020, times = 12), 
  Country = rep(c("ABW", "AFG", "AGO", "AIA", "ALB", "AND", "ANT", "ARE", "ARG", "ARM", "AUT", "ETH"), each = 26), 
  deg_in_norm = runif(12 * 26, min = 0, max = 1), 
  deg_out_norm = runif(12 * 26, min = 0, max = 1) 
)

highlighted_countries <- c("ZAF", "SAU", "RUS", "IRN", "IND", "ETH", "EGY", "CHN", "BRA", "ARG", "ARE")
temp <- temp %>%
  mutate(Color = ifelse(Country %in% highlighted_countries, as.character(Country), "Not BRICS")) %>%
  mutate(Size = ifelse(Country %in% highlighted_countries, 1, 0)) %>%
  mutate(Full_names = ifelse(Country %in% highlighted_countries, 
                             countrycode(Country, origin = 'iso3c', destination = 'country.name'), 
                             "Not BRICS")) %>%
  group_by(Country) %>%
  mutate(id = cur_group_id()) %>%
  ungroup()

ggplot(data = temp) +
  geom_line(aes(x = Year, y = deg_in_norm, 
                color = factor(Color), size = factor(Size), group = id)) +
  scale_color_manual(values = c("ARE" = "black", "ARG" = "#6699CC", "ETH" = "#44AA99",
                                "Not BRICS" = "grey"),
                     labels = c("United Arab Emirates", "Argentina", "Ethiopia",
                                "Not BRICS")) +
  scale_size_manual(values = c("0" = 0.5, "1" = 1.5), guide = "none") + 
  guides(color = guide_legend(
    override.aes = list(size = 3),  # 设置图例线条粗细（推荐3-5区间）
    keywidth = unit(2, "cm"),       # 加宽图例key区域，让粗线条更清晰
    keyheight = unit(0.5, "cm")     # 调整key区域高度，优化视觉效果
  )) +  
  theme(legend.position = "bottom") +
  labs(y = "Normalised In-Degree\n")

关键调整说明 #

• 修正了dplyr管道符的语法错误（%>改为%>%）。
• 将override.aes中的size改为合理数值，避免图例区域过度放大。
• 添加keywidth和keyheight参数，调整图例key的尺寸，让加粗后的线条更易区分。
• 保留了你原本的size映射逻辑（高亮国家线条更粗），同时确保图例线条的加粗效果清晰呈现。

内容的提问来源于stack exchange，提问作者Djoustaine