R ggplot 适合图例大小到绘图大小

正如@benson23在 comments 中所建议的那样，@teunbrand对你的问题给出了一个非常好的答案:Set legend width to be 100% plot width.如果使用该代码，它将如下所示:

#plot:
pp = ggplot(data) + 
  geom_raster(aes(x=x,y=y,fill = val)) +
  scale_fill_continuous(guide = guide_colorbar(barwidth = unit(4,'cm'))) + 
  theme(legend.direction = 'horizontal',legend.position = 'bottom') 
pp

gt <- ggplotGrob(pp) 

# Extract legend
is_legend <- which(gt$layout$name == "guide-box")
legend <- gt$grobs[is_legend][[1]]
legend <- legend$grobs[legend$layout$name == "guides"][[1]]

# Set widths in guide gtable
width <- as.numeric(legend$widths[4]) # save bar width (assumes 'cm' unit) 
legend$widths[4] <- unit(1, "null") # replace bar width

# Set width/x of bar/labels/ticks. Assumes everything is 'cm' unit.
legend$grobs[[2]]$width <- unit(1, "npc")
legend$grobs[[3]]$children[[1]]$x <- unit(
  as.numeric(legend$grobs[[3]]$children[[1]]$x) / width, "npc"
)
legend$grobs[[5]]$x0 <- unit(as.numeric(legend$grobs[[5]]$x0) / width, "npc")
legend$grobs[[5]]$x1 <- unit(as.numeric(legend$grobs[[5]]$x1) / width, "npc")

# Replace legend
gt$grobs[[is_legend]] <- legend

# Draw new plot
grid::grid.newpage()
grid::grid.draw(gt)

输出: