r - R中箱线图中的上下四分位数

Question

我有

X=c(20 ,18, 34, 45, 30, 51, 63, 52, 29, 36, 27, 24)

使用 boxplot，我试图绘制 quantile(X,0.25)和 quantile(X,0.75)但这与R中的箱形图的上下四分位数并不完全相同

boxplot(X)
abline(h=quantile(X,0.25),col="red",lty=2)
abline(h=quantile(X,0.75),col="red",lty=2)

你知道为什么吗？

Answer 1

框的值称为铰链，可能与四分位数重合(由quantile(x, c(0.25, .075))计算)，但计算方式不同。

从?boxplot.stats:

The two ‘hinges’ are versions of the first and third quartile, i.e., close to quantile(x, c(1,3)/4). The hinges equal the quartiles for odd n (where n <- length(x)) and differ for even n. Whereas the quartiles only equal observations for n %% 4 == 1 (n = 1 mod 4), the hinges do so additionally for n %% 4 == 2 (n = 2 mod 4), and are in the middle of two observations otherwise.

要查看这些值与奇数个观测值一致，请尝试以下代码:

set.seed(1234)
x <- rnorm(9)

boxplot(x)
abline(h=quantile(x, c(0.25, 0.75)), col="red")