ggplot2:图下方的中心图例，而不是面板区域 [英] ggplot2: center legend below plot instead of panel area

问题描述

ggplot将图例置于面板下方，这在某些情况下确实令人沮丧.请参见以下示例:

ggplot by default centers the legend below the panel, which is really frustrating in some situations. Please see the below example:

ggplot(diamonds, aes(cut, fill = clarity)) + geom_bar() + coord_flip() + 
  theme(legend.position = 'bottom')

可以看到，最后一个标签是从图像中裁剪出来的，尽管图例的左侧有一些空白-使用它会更好.

It can be seen that the last label was cropped from the image, although we have some white-space on the left part of the legend -- it would be a lot better to use that.

问:如何将图例居中放置在图的下方，而不尝试强制将图例居中放置在面板区域的下方，以解决此问题?

Q: how can I center the legend below the plot and not try to force that to be centered below the panel area to overcome this issue?

更新:此问题的进一步示例:

Update: further example on this issue:

df <- data.frame(
    x = sample(paste('An extremely long category label that screws up legend placement', letters[1:7]), 1e3, TRUE),
    y = sample(paste('Short label', letters[1:7]), 1e3, TRUE)
    )

ggplot(df, aes(x, fill = y)) + geom_bar() + coord_flip() +
  theme(legend.position = 'bottom')

我所做的事情:我可以使用legend.direction手动将图例放在面板下方，并在绘图下方添加一些额外的边距，例如:

What I've done: I can use legend.direction to manually put the legend below the panel and to add some extra margin below the plot, like:

ggplot(diamonds, aes(cut, fill = clarity)) + geom_bar() + coord_flip() + 
  theme(legend.position  = c(0.37, -0.1),
        legend.direction = 'horizontal',
        plot.margin      = grid::unit(c(0.1,0.1,2,0.1), 'lines'))

但是这种方式我必须手动"计算最佳legend.position.有什么建议吗?

But this way I have to compute "manually" the optimal legend.position. Any suggestions?

更新:我正在将多个图并排布置，所以我宁愿不要将图例放在实际图像上居中，而要在单个面板上居中.例如:

Update: I am arranging multiple plots next to each other, so I'd rather not center the legend on the actual image, but rather on the single panel. E.g.:

p1 <- ggplot(diamonds, aes(cut)) + geom_histogram()
p2 <- ggplot(diamonds, aes(cut, fill = clarity)) + geom_bar() + coord_flip() +
  theme(legend.position = 'bottom')
pushViewport(viewport(layout = grid.layout(nrow = 1, ncol = 2, widths = unit(c(1, 2), c("null", "null")))))
print(p1, vp = viewport(layout.pos.row = 1, layout.pos.col = 1))
print(p2, vp = viewport(layout.pos.row = 1, layout.pos.col = 2))

推荐答案

您可以编辑gtable，

you can edit the gtable,

library(gtable)

g <- ggplotGrob(p)
id <- which(g$layout$name == "guide-box")
g$layout[id, c("l","r")] <- c(1, ncol(g))
grid.newpage()
grid.draw(g)

这篇关于ggplot2:图下方的中心图例，而不是面板区域的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！