在 R 中标记箱线图的异常值

问题描述

我有创建箱线图的代码，在 R 中使用 ggplot，我想用年份和 Battle 标记我的异常值.

I have the code that creates a boxplot, using ggplot in R, I want to label my outliers with the year and Battle.

这是我创建箱线图的代码

Here is my code to create my boxplot

require(ggplot2)
ggplot(seabattle, aes(x=PortugesOutcome,y=RatioPort2Dutch ),xlim="OutCome",
y="Ratio of Portuguese to Dutch/British ships") +
geom_boxplot(outlier.size=2,outlier.colour="green") +
stat_summary(fun.y="mean", geom = "point", shape=23, size =3, fill="pink") +
ggtitle("Portugese Sea Battles")

有人可以帮忙吗?我知道这是正确的，我只想标记异常值.

Can anyone help? I knew this is correct, I just want to label the outliers.

推荐答案

以下是使用 dplyr 和内置 mtcars 数据集的可重现解决方案.

The following is a reproducible solution that uses dplyr and the built-in mtcars dataset.

遍历代码:首先，创建一个函数，is_outlier，如果传递给它的值是异常值，它将返回一个布尔值TRUE/FALSE.然后我们执行分析/检查"并绘制数据——首先我们group_by我们的变量(在这个例子中是cyl，在你的例子中，这将是PortugesOutcome) 并且我们在对 mutate 的调用中添加一个变量 outlier(如果 drat 变量是一个异常值 [注意这对应到 RatioPort2Dutch in your example]，我们将传递 drat 值，否则我们将返回 NA 以便不绘制该值).最后，我们绘制结果并通过 geom_text 和一个与我们的新变量相等的美学标签绘制文本值；此外，我们使用 hjust 偏移文本(将其向右滑动一点)，以便我们可以看到离群点旁边而不是顶部的值.

Walking through the code: First, create a function, is_outlier that will return a boolean TRUE/FALSE if the value passed to it is an outlier. We then perform the "analysis/checking" and plot the data -- first we group_by our variable (cyl in this example, in your example, this would be PortugesOutcome) and we add a variable outlier in the call to mutate (if the drat variable is an outlier [note this corresponds to RatioPort2Dutch in your example], we will pass the drat value, otherwise we will return NA so that value is not plotted). Finally, we plot the results and plot the text values via geom_text and an aesthetic label equal to our new variable; in addition, we offset the text (slide it a bit to the right) with hjust so that we can see the values next to, rather than on top of, the outlier points.

library(dplyr)
library(ggplot2)

is_outlier <- function(x) {
  return(x < quantile(x, 0.25) - 1.5 * IQR(x) | x > quantile(x, 0.75) + 1.5 * IQR(x))
}

mtcars %>%
  group_by(cyl) %>%
  mutate(outlier = ifelse(is_outlier(drat), drat, as.numeric(NA))) %>%
  ggplot(., aes(x = factor(cyl), y = drat)) +
    geom_boxplot() +
    geom_text(aes(label = outlier), na.rm = TRUE, hjust = -0.3)

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