r - 将线段添加到密度图

Question

我想在我的图中添加一条线来指示平均值:

X1 <- rnorm(100)
# Kernel density estimates
density_X1 <- density(X1)
# Compute mode
mode_X1 <- density_X1$x[which.max(density_X1$y)]; mode_X1
# Compute mean
mean_X1 <- mean(X1)
# Create plot 
plot(density_X1, main = "Kernel density estimates", xlab = "X1", ylab = "density")
# Add line for mode
segments(x0 = mode_X1, y0 = 0, x1 = mode_X1, y1 = density_X1$y, col = "red", lty = 1, lwd = 1)
# Add line for mean
segments(x0 = mean_X1, y0 = 0, x1 = mean_X1, y1 = , col = "red", lty = 5, lwd = 2)

我需要为segments(y1 = )输入什么值才能确保上限是核密度图？

Answer 1

要根据离散点的密度估计计算某个 x 值的 y 值，您需要进行某种插值。一种方法是使用 approx 的线性插值:

approx(x = density_X1$x, y = density_X1$y, xout = mean_X1)$y

其中，x 和 y 给出要插值的点，xout 是插值的 x 值(向量)完成(参见？大约)

所以代码总共是:

set.seed(72405277)
X1 <- rnorm(100)
# Kernel density estimates
density_X1 <- density(X1)
# Compute mode
mdIdx <- which.max(density_X1$y) # store and resuse
mode_X1 <- density_X1$x[mdIdx]; 
# Compute mean
mean_X1 <- mean(X1)
# Create plot 
plot(density_X1, main = "Kernel density estimates", xlab = "X1", ylab = "density")
# Add line for mode
segments(x0 = mode_X1, y0 = 0, x1 = mode_X1, y1 = density_X1$y[mdIdx], col = "red", lty = 1, lwd = 1)
# Add line for mean
yax2 <- approx(x = density_X1$x, y = density_X1$y, xout = mean_X1)$y
segments(x0 = mean_X1, y0 = 0, x1 = mean_X1, y1 = yax2, col = "blue", lty = 5, lwd = 2)