ggplot2：如何在图例的两条虚线之间添加间隔？

问题描述 #

我用以下代码生成了两幅直方图，希望找到简单方法在直方图图例的虚线之间添加间隔，避免虚线互相接触。我曾尝试在theme部分添加legend.spacing.y，但仅实现了整个图例的下移，无法达成目标。

原代码 #

#make low cost histogram

PLOT1 <- LCset1 %>% 
  ggplot(aes(x=donation, fill=lowmonetaryamount))+
  coord_cartesian(xlim = c(1, NA)) +
  geom_histogram(binwidth=1,aes(y = (..count..)/sum(..count..)),col=I("black"))+
  scale_color_grey()+scale_fill_grey(start = .85,
                                     end = .85,) +
  theme_linedraw()+
  guides(fill = "none", cols='none')+
  geom_vline(aes(xintercept=10, size='
Low cost
'),
             color="black", linetype=5)+
  geom_vline(aes(xintercept=50, size='
High cost
'),
             color="black", linetype="dotted")+
  scale_size_manual(values = c(.5, 0.5), breaks = c('
Low cost
','
High cost
'), guide=guide_legend(title = "", override.aes = list(linetype=c(5,3), color=c('black', 'black'))))+
  scale_y_continuous(labels=scales::percent, limits = c(0, .015))+
  scale_x_continuous(breaks = c(seq(0,50,10), 55), labels = c("","$10","$20","$30","$40","$50","      >$50"), limits = c(0, 60))+
  ggtitle("
% donating each non-zero amount when low cost is $10")+
  theme(plot.title = element_text(hjust = 0.5))+
  xlab(NULL)+
  ylab(NULL)+
  theme(plot.title = element_text(size=13))+
  theme(
    # other theme parameters
    legend.key.size = unit(2, "lines"),     
    legend.key.width = unit(1, "lines"),
    legend.text = element_text(size=12),
    axis.text = element_text(size=12),
    legend.key.height = unit(0.5, "lines")
  )

#make high cost histogram 

PLOT2 <- HCset1 %>% 
  ggplot(aes(x=donation, fill=lowmonetaryamount))+
  coord_cartesian(xlim = c(1, NA)) +
  geom_histogram(binwidth=1,aes(y = (..count..)/sum(..count..)),col=I("black"))+
  scale_color_grey()+scale_fill_grey(start = .85,
                                     end = .85,) +
  theme_linedraw()+
  guides(fill = "none", cols='none')+
  geom_vline(aes(xintercept=10, size='
Low cost
'),
             color="black", linetype=5)+
  geom_vline(aes(xintercept=50, size='
High cost
'),
             color="black", linetype="dotted")+
  scale_size_manual(values = c(.5, 0.5), breaks = c('
Low cost
','
High cost
'), guide=guide_legend(title = "", override.aes = list(linetype=c(5,3), color=c('black', 'black'))))+
  scale_y_continuous(labels=scales::percent, limits = c(0, .015))+
  scale_x_continuous(breaks = c(seq(0,50,10), 55), labels = c("","$10","$20","$30","$40","$50","      >$50"), limits = c(0, 60))+
  ggtitle("% donating each non-zero amount when high cost is $50")+
  theme(plot.title = element_text(hjust = 0.5))+
  xlab(NULL)+
  ylab(NULL)+
  theme(plot.title = element_text(size=13))+
  theme(
    # other theme parameters
    legend.key.size = unit(2, "lines"),     
    legend.key.width = unit(1, "lines"),
    legend.text = element_text(size=12),
    axis.text = element_text(size=12),
    legend.key.height = unit(0.5, "lines")
  )

#combine two histograms

plot<- ggarrange(PLOT1, PLOT2,ncol=1,label.x=1,common.legend = TRUE, legend="right")
plots <- grid.arrange(plot,top=textGrob("Histograms for the 40.1% of the total sample whose last donation was between $10.00 and $49.99",gp=gpar(fontsize=14,fontface="bold")))

ggsave("plots_1.png", plots, width = 10, height = 8)

解决方案 #

要让图例中的两条虚线条目分离，需要同时调整图例条目间距和每个图例key的垂直高度，还要清理代码中多余的换行：

1. 调整图例间距与key高度：在theme()中，设置legend.spacing.y为正数单位来增加条目间空隙，同时增大legend.key.height确保每个key有足够空间。
2. 清理多余换行：移除geom_vline和scale_size_manual中标签文本的多余换行，避免图例排版混乱。

修改后的核心代码片段 #

# 替换PLOT1和PLOT2中的theme部分
theme(
  legend.key.size = unit(2, "lines"),     
  legend.key.width = unit(1, "lines"),
  legend.text = element_text(size=12),
  axis.text = element_text(size=12),
  legend.key.height = unit(1, "lines"),  # 增大key的垂直高度
  legend.spacing.y = unit(1, "lines")    # 添加条目间的垂直间隔
)

# 替换geom_vline的size标签，移除多余换行
geom_vline(aes(xintercept=10, size='Low cost'),
           color="black", linetype=5)+
geom_vline(aes(xintercept=50, size='High cost'),
           color="black", linetype="dotted")

# 替换scale_size_manual的breaks参数，移除多余换行
scale_size_manual(
  values = c(.5, 0.5), 
  breaks = c('Low cost','High cost'), 
  guide=guide_legend(
    title = "", 
    override.aes = list(linetype=c(5,3), color=c('black', 'black'))
  )
)

修改后，图例中的两条虚线会被明显的垂直间隔分开，不会再互相接触。

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