特定值上方和下方的 geom_line 的不同颜色 [英] Different colours of geom_line above and below a specific value

问题描述

我有以下要绘制的数据框.我想知道是否可以将连接我的结果变量(stackOne$y)的部分线条着色为不同的颜色，具体取决于它是否小于某个值.例如，我希望低于 2.2 的线条部分为红色.

I have the following dataframe that I would like to plot. I was wondering if it is possible to color portions of the lines connecting my outcome variable(stackOne$y) in a different color, depending on whether it is less than a certain value or not. For example, I would like portions of the lines falling below 2.2 to be red in color.

set.seed(123)
stackOne = data.frame(id = rep(c(1, 2, 3), each = 3),
                     y = rnorm(9, 2, 1),
                     x = rep(c(1, 2, 3), 3))

ggplot(stackOne, aes(x = x, y = y)) +
    geom_point() +
    geom_line(aes(group = id))

谢谢！

推荐答案

这里至少有几个选项.第一个非常简单、通用(因为它不限于直线段)和精确，但使用基础 plot 而不是 ggplot.第二个使用 ggplot，但稍微复杂一些，颜色过渡不会 100% 精确(但足够接近，只要您指定适当的分辨率...继续阅读).

You have at least a couple of options here. The first is quite simple, general (in that it's not limited to straight-line segments) and precise, but uses base plot rather than ggplot. The second uses ggplot, but is slightly more complicated, and colour transition will not be 100% precise (but near enough, as long as you specify an appropriate resolution... read on).

基础:

如果您愿意使用 base 绘图函数而不是 ggplot，您可以将绘图区域裁剪到阈值 (2.2) 以上，然后在您喜欢的颜色，然后剪辑到阈值以下的区域，并再次绘制为红色.虽然第一个剪辑完全没有必要，但它可以防止过度绘制不同的颜色，这可能看起来有点乏味.

If you're willing to use base plotting functions rather than ggplot, you could clip the plotting region to above the threshold (2.2), then plot the segments in your preferred colour, and subsequently clip to the region below the threshold, and plot again in red. While the first clip is strictly unnecessary, it prevents overplotting different colours, which can look a bit dud.

threshold <- 2.2
set.seed(123)
stackOne=data.frame(id=rep(c(1,2,3),each=3),
                y=rnorm(9,2,1),
                x=rep(c(1,2,3),3))
# create a second df to hold segment data
d <- stackOne 
d$y2 <- c(d$y[-1], NA)
d$x2 <- c(d$x[-1], NA) 
d <- d[-findInterval(unique(d$id), d$id), ] # remove last row for each group

plot(stackOne[, 3:2], pch=20)
# clip to region above the threshold
clip(min(stackOne$x), max(stackOne$x), threshold, max(stackOne$y))
segments(d$x, d$y, d$x2, d$y2, lwd=2)
# clip to region below the threshold
clip(min(stackOne$x), max(stackOne$x), min(stackOne$y), threshold)
segments(d$x, d$y, d$x2, d$y2, lwd=2, col='red')
points(stackOne[, 3:2], pch=20) # plot points again so they lie over lines

ggplot:

如果你想或需要使用ggplot，你可以考虑以下...

If you want or need to use ggplot, you can consider the following...

一种解决方案是使用 geom_line(aes(group=id, color = y < 2.2))，但是这将根据起始点的 y 值分配颜色每个段.我相信您不仅希望在节点处改变颜色，而且希望在任何一条线越过给定阈值 2.2 的地方改变颜色.我对 ggplot 不是很熟悉，但实现这一点的一种方法是通过沿着连接现有点的线创建新点来制作更高分辨率版本的数据，然后使用 color = y<2.2参数达到预期效果.

One solution is to use geom_line(aes(group=id, color = y < 2.2)), however this will assign colours based on the y-value of the point at the beginning of each segment. I believe you want to have the colour change not just at the nodes, but wherever a line crosses your given threshold of 2.2. I'm not all that familiar with ggplot, but one way to achieve this is to make a higher-resolution version of your data by creating new points along the lines that connect your existing points, and then use the color = y < 2.2 argument to achieve the desired effect.

例如:

threshold <- 2.2 # set colour-transition threshold
yres <- 0.01 # y-resolution (accuracy of colour change location)

d <- stackOne # for code simplification
# new cols for point coordinates of line end
d$y2 <- c(d$y[-1], NA)
d$x2 <- c(d$x[-1], NA) 
d <- d[-findInterval(unique(d$id), d$id), ] # remove last row for each group
# new high-resolution y coordinates between each pair within each group
y.new <- apply(d, 1, function(x) {
  seq(x['y'], x['y2'], yres*sign(x['y2'] - x['y']))
})
d$len <- sapply(y.new, length) # length of each series of points
# new high-resolution x coordinates corresponding with new y-coords
x.new <- apply(d, 1, function(x) {
  seq(x['x'], x['x2'], length.out=x['len'])
})
id <- rep(seq_along(y.new), d$len) # new group id vector
y.new <- unlist(y.new)
x.new <- unlist(x.new)
d.new <- data.frame(id=id, x=x.new, y=y.new)

p <- ggplot(d.new, aes(x=x,y=y)) +
  geom_line(aes(group=d.new$id, color=d.new$y < threshold))+
  geom_point(data=stackOne)+
  scale_color_discrete(sprintf('Below %s', threshold))
p

很可能有一种方法可以通过 ggplot 函数来做到这一点，但同时我希望这会有所帮助.我不知道如何将 ggplotGrob 绘制到剪切的 viewport 中(而它似乎只是缩放绘图).如果您希望颜色以某个 x 值阈值为条件，这显然需要进行一些调整.

There may well be a way to do this through ggplot functions, but in the meantime I hope this helps. I couldn't work out how to draw a ggplotGrob into a clipped viewport (rather it seems to just scale the plot). If you want colour to be conditional on some x-value threshold instead, this would obviously need some tweaking.

这篇关于特定值上方和下方的 geom_line 的不同颜色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！