ggplot2 0.9.3及更高版本中美学的继承comment_custom的行为 [英] inheritance of aesthetics in ggplot2 0.9.3 & the behavior of annotation_custom

问题描述

紧随最近的问题 mine ，这个问题有点不同，并使用更简单的示例更全面地说明了该问题.以下是两个数据集和三个功能.第一个按预期绘制了一些点和一个圆:

Following up on a recent question of mine, this one is a bit different and illustrates the problem more fully using simpler examples. Below are two data sets and three functions. The first one draws some points and a circle as expected:

library("ggplot2")
library("grid")

td1 <- data.frame(x = rnorm(10), y = rnorm(10))

tf1 <- function(df) { # works as expected
    p <- ggplot(aes(x = x, y = y), data = df)
    p <- p + geom_point(color = "red")
    p <- p + annotation_custom(circleGrob())
    print(p)
}

tf1(td1)

下一个似乎要求提供确切的样图，但代码略有不同.它不会给出错误，但不会画出圆圈:

This next one seems to ask for the exact sample plot but the code is slightly different. It does not give an error but does not draw the circle:

tf2 <- function(df) { # circle isn't draw, but no error either
    p <- ggplot()
    p <- p + geom_point(data = df, aes(x = x, y = y), color = "red")        
    p <- p + annotation_custom(circleGrob())
    print(p)
    }

tf2(td1)

最后，这涉及一种更复杂的美学，并在您尝试创建圆时提供了一个空白层:

Finally, this one involves a more complex aesthetic and gives an empty layer when you try to create the circle:

td3 <- data.frame(r = c(rnorm(5, 5, 1.5), rnorm(5, 8, 2)),
    f1 = c(rep("L", 5), rep("H", 5)), f2 = rep(c("A", "B"), 5))

tf3 <- function(df) {
    p <- ggplot()
    p <- p + geom_point(data = df, 
        aes(x = f1, y = r, color = f2, group = f2))     
#   p <- p + annotation_custom(circleGrob()) # comment out and it works
    print(p)
    }

tf3(td3)

现在，我怀疑这里的问题不是代码，而是我无法掌握ggplot2的内部工作原理. 我可以肯定地解释一下为什么在第二种情况下没有画圆，以及为什么在第三种情况下该层是空的.我查看了annotation_custom的代码，它很难我认为这是有线inherit.aes = TRUE的问题.我不明白为什么此功能根本不需要任何美感(请参阅有关它的文档).我确实尝试了几种方法来覆盖它并设置inherit.aes = FALSE，但是我无法完全穿透名称空间并使它保持不变.我试图以ggplot2创建的对象为例，但是这些proto对象嵌套得非常深，难以破解.

Now, I suspect the problem here is not the code but my failure to grasp the inner workings of ggplot2. I could sure use an explanation of why the circle is not drawn in the 2nd case and why the layer is empty in the third case. I looked at the code for annotation_custom and it has a hard-wired inherit.aes = TRUE which I think is the problem. I don't see why this function needs any aesthetic at all (see the docs on it). I did try several ways to override it and set inherit.aes = FALSE but I was unable to fully penetrate the namespace and make it stick. I tried to example the objects created by ggplot2 but these proto objects are nested very deeply and hard to decipher.

推荐答案

要回答这个问题:

我不明白为什么该功能根本不需要任何美感."

"I don't see why this function needs any aesthetic at all".

实际上，annotation_custom需要x和y aes来缩放其grob，并在native个单位之后使用. 基本上是这样做的:

In fact annotation_custom need x and y aes to scale its grob, and to use after the native units. Basically it did this :

  x_rng <- range(df$x, na.rm = TRUE)                            ## ranges of x :aes x
  y_rng <- range(df$y, na.rm = TRUE)                            ## ranges of y :aes y
  vp <- viewport(x = mean(x_rng), y = mean(y_rng),              ##  create a viewport
                 width = diff(x_rng), height = diff(y_rng),
                 just = c("center","center"))
  dd <- editGrob(grod =circleGrob(), vp = vp)                  ##plot the grob in this vp 

为了说明这一点，我在一个虚拟图上添加了一个grob，用作我的grob的比例.第一个是大规模，第二个是小规模.

To illustrate this I add a grob to a dummy plot used as a scale for my grob. The first is a big scale and the second is a small one.

base.big   <- ggplot(aes(x = x1, y = y1), data = data.frame(x1=1:100,y1=1:100))
base.small <- ggplot(aes(x = x1, y = y1), data = data.frame(x1=1:20,y1=1:1))

我定义了我的grob，请参见我使用xmin，xmax，ymin，ymax的本机刻度

I define my grob, see I use the native scales for xmin,xmax,ymin,ymax

annot <- annotation_custom(grob = circleGrob(),  xmin = 0, 
                                                 xmax = 20, 
                                                 ymin = 0, 
                                                 ymax = 1)

现在可以看到(base.big +annot)和(base.small + annot)之间的比例差异(小点/大圆圈).

Now see the scales difference(small point / big circle) between (base.big +annot) and (base.small + annot).

library(gridExtra)
grid.arrange(base.big+annot,
             base.small+annot)

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