在拼面图中为单个面板添加几何图层

Question

从以下链接Aligning two plots with ggplot2中获取提示，我能够绘制针对公共x轴的2个“y”变量。我现在要做的是能够只将geom_point图层添加到其中一个方面。该图层使用与d1具有相同结构的不同数据集（d3）。当我添加图层时，它会在两个方面上使用。是否可以仅将点分层为上方。

library(ggplot2)

x <- seq(1992, 2002, by = 2)
d1 <- data.frame(x = x, y = rnorm(length(x)))
xy <- expand.grid(x = x, y = x)
d2 <- data.frame(x = xy$x, y = xy$y, z = jitter(xy$x + xy$y))
d3 <- data.frame(x = x, y = 3+rnorm(length(x)))

d1$panel <- "a"
d2$panel <- "b"
d1$z <- d1$x

d <- rbind(d1, d2)

p <- ggplot(data = d, mapping = aes(x = x, y = y))
p <- p + facet_grid(panel ~ ., scale = "free")
p <- p + layer(data = d1,  geom = c( "line"), stat = "identity")
###*p <- p + layer(data = d3,  geom = c( "point"))* - This is the layer I intend to add only to the top panel

p <- p + layer(data = d2,  geom = "line", stat = "identity")
p

Answer 1

只需将panel列添加到d3，并添加要添加点集的面板即可。在你的情况下：

d3$panel = "a"

p <- ggplot(data = d, mapping = aes(x = x, y = y))
p <- p + facet_grid(panel ~ ., scale = "free")
p <- p + layer(data = d1,  geom = c( "line"), stat = "identity")
p <- p + layer(data = d3,  geom = c( "point"))
p <- p + layer(data = d2,  geom = "line", stat = "identity")
p

产生正确的输出：

如果facet_grid调用中提到的列不存在，ggplot2会假定需要在所有方面打印。当您指定panel时，ggplot2会将其考虑在内。