以给定角度旋转 R 中箱线图的 x 轴标签

Question

我用下面的代码生成了一个箱线图：

boxplot(top10threads$affect ~ top10threads$ThreadID[], data = top10threads, xlab = "10 biggest Threads", ylab = "Affect", col=(c("gold","darkgreen")), srt=45)

但是您可能会注意到 x 轴上的一些标签丢失了，所以我想将它们旋转 45 度。我加了srt=45，但是不行。

通过设置las=2 可以垂直旋转它们，但这并不完全是我需要的。

我怎么能这样做？谢谢。

Answer 1

首先，将boxplot() 的输出存储为对象。它包含组的名称。您可以使用$names 来获取它们。然后使用text() 添加轴的标签。参数 srt 适用于 text()。

tmp <- boxplot(y ~ x, data = df, col = c("gold","darkgreen"), xaxt = "n")
tick <- seq_along(tmp$names)
axis(1, at = tick, labels = F)
text(tick, par("usr")[3] - 0.3, tmp$names, srt = 45, xpd = T)

---

数据

df <- data.frame(x = sample(100:110, 100, T), y = rnorm(100))

Answer 2

一些测试数据：

mydata=lapply(1:5,function(i) rnorm(100,mean=i))
names(mydata)=c("first","second","third","fourth","fifth")

首先，绘制没有 x 轴的箱线图：

boxplot(mydata,xaxt="n",xlab="")

然后，我们创建一个函数来添加文本 x 轴标签：

x_axis_labels=function(labels,every_nth=1,...) {
    axis(side=1,at=seq_along(labels),labels=F)
    text(x=(seq_along(labels))[seq_len(every_nth)==1],
        y=par("usr")[3]-0.075*(par("usr")[4]-par("usr")[3]),
        labels=labels[seq_len(every_nth)==1],xpd=TRUE,...)
}
# axis() draws the axis with ticks at positions specified by at.  Again, we don't plot the labels yet.
# text() plots the labels at positions given by x and y.
# We estimate the y-positions from the values of the y-axis (using par("usr")),
# and specify xpd=TRUE to indicate that we don't want to crop plotting to within the plot area
# Note that we select the [seq_len(every_nth)==1] elements of both the x positions and the labels, 
# so we can easily skip labels if there would be too many to cram in otherwise.  
# Finally, we leave a ... in the function so we can pass additional arguments to text()

最后，我们调用新函数来绘制轴刻度标签：

x_axis_labels(labels=names(mydata),every_nth=1,adj=1,srt=45)

这里我们利用函数中的 ... 来传递旋转/对齐参数：adj=1 表示将文本标签右对齐，srt=45 表示将它们旋转 45 度。