R ggplot2:使用 stat_summary(平均值)和对数刻度 [英] R ggplot2: using stat_summary (mean) and logarithmic scale

问题描述

随着时间的推移，我有一堆测量值，我想在 R 中绘制它们.这是我的数据示例.我有 4 个时间点中的每一个的 6 个测量值:

I have a bunch of measurements over time and I want to plot them in R. Here is a sample of my data. I've got 6 measurements for each of 4 time points:

values <- c (1012.0, 1644.9, 837.0, 1200.9, 1652.0, 981.5, 
    2236.9, 1697.5, 2087.7, 1500.8,
    2789.3, 1502.9, 2051.3, 3070.7, 3105.4, 
    2692.5, 1488.5, 1978.1, 1925.4, 1524.3,
    2772.0, 1355.3, 2632.4, 2600.1)
time <- factor (rep (c(0, 12, 24, 72), c(6, 6, 6, 6)))

这些数据的规模是任意的，实际上我将对其进行标准化，以便 t=0 的平均值为 1.

The scale of these data is arbitrary, and in fact I'm going to normalize it so that the average of t=0 is 1.

norm <- values / mean (values[time == 0])

到目前为止一切顺利.使用 ggplot，我绘制了各个点以及穿过每个时间点平均值的线:

So far so good. Using ggplot, I plot both the individual points, as well as a line that goes through the average at each time point:

require (ggplot2)
p <- ggplot(data = data.frame(time, norm), mapping = aes (x = time, y = norm)) +
    stat_summary (fun.y = mean, geom="line", mapping = aes (group = 1)) +
    geom_point()

然而，现在我想应用对数刻度，这就是我的麻烦开始的地方.当我这样做时:

However, now I want to apply a logarithmic scale, and this is where my trouble starts. When I do:

q <- ggplot(data = data.frame(time, norm), mapping = aes (x = time, y = norm)) +
    stat_summary (fun.y = mean, geom="line", mapping = aes (group = 1)) +
    geom_point() + 
    scale_y_log2()

该线在 t=0 时不会像您期望的那样通过 0，因为 log (1) == 0.相反，该线与 y 轴的交叉点略低于 0.显然，ggplot在对数转换之后应用平均值，这给出了不同的结果.我希望它取平均值 before 对数转换.

The line does NOT go through 0 at t=0, as you would expect because log (1) == 0. Instead the line crosses the y-axis slightly below 0. Apparently, ggplot applies the mean after log transformation, which gives a different result. I want it to take the mean before log transformation.

如何告诉 ggplot 先应用平均值?有没有更好的方法来创建这个图表?

How can I tell ggplot to apply the mean first? Is there a better way to create this chart?

推荐答案

scale_y_log2() 会先做转换，然后计算几何.

scale_y_log2() will do the transformation first and then calculate the geoms.

coord_trans() 将做相反的事情:首先计算几何图形，然后变换轴.

coord_trans() will do the opposite: calculate the geoms first, and the transform the axis.

所以你需要 coord_trans(ytrans = "log2") 而不是 scale_y_log2()

So you need coord_trans(ytrans = "log2") instead of scale_y_log2()

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