r - 垂直线在 ggplot 中未按预期显示

Question

我正在模拟 40 个独立同分布指数的均值分布，并绘制样本均值的分布以及样本均值 (A) 的分布均值和 lambda = 0.2 (B) 的指数的理论均值。这两种方法 A 和 B 应显示为不同颜色的垂直线，并且应在图例中解释它们的颜色代码。然而，我的代码只产生一条垂直线，并忽略了我在代码中定义的配色方案。

代码如下：

n <- 40

lambda <- 0.2

simulation = data.table(sample_mean = numeric())

for (i in (1 : 1000)){
  simulation <- rbind(simulation, data.table(sample_mean = mean(rexp(n,  lambda))))
}

#==============================================================================================
# Show the sample mean and compare it to the theoretical mean of the distribution.
#==============================================================================================

sample_mean <- mean(simulation$sample_mean)
4.981267

theoretical_mean <- 1/lambda
5

#------------------------------------------------------------------------------------------
# Plot of the Empirical and Theoretical Distributions and their respective means
#------------------------------------------------------------------------------------------

ggplot(simulation, aes(x = sample_mean) ) +
geom_histogram(aes(y=..density..), position="identity",alpha = 0.4, fill = "red", bins=100) +
  geom_density(colour = "red" , size = 2, alpha = 0.5) +
  geom_vline(xintercept = sample_mean, aes(colour = "Empirical"), size = 1.5, alpha =0.3) +
  geom_vline(xintercept = lambda, aes(colour = "Theoretical"), size = 1.5, alpha =0.3) +
  theme_economist() + ggtitle("Distribution of Sample Means.  Mean of the Empirical Distribution 
  and Mean of the Theoretical Exponential (1,000 simulations) ") +
  scale_colour_manual("Distributions", values = c("blue", "red")) +
  scale_y_continuous(name = "Density") +   
  scale_x_continuous(name = "Sample Means", breaks = seq(2, 8, .5), limits=c(2, 8))

情节如下：

您的建议将不胜感激。

====================================

编辑

@mkt：感谢您的贡献。我仍然需要在图中注释垂直线，这就是为什么我使用 aes() 中的颜色以及稍后在我的代码中映射到颜色的字符串。所以我仍然需要找到如何做到这一点的解决方案。

Answer 1

你遇到了三个问题。1）您正在绘制 lambda，而不是 1/lambda 2）“经验”和“理论”不是 R 将识别的颜色 3）颜色不应在 aes() 中定义

这有效：

ggplot(simulation, aes(x = sample_mean) ) +
  geom_histogram(aes(y=..density..), position="identity",alpha = 0.4, fill = "red", bins=100) +
  geom_density(colour = "red" , size = 2, alpha = 0.5) +
  geom_vline(xintercept = sample_mean, colour = "blue", size = 1.5, alpha = 0.3) +
  geom_vline(xintercept = theoretical_mean, colour = "green", size = 1.5, alpha = 0.5) +
  ggtitle("Distribution of Sample Means.  Mean of the Empirical Distribution 
  and Mean of the Theoretical Exponential (1,000 simulations) ") +
  scale_colour_manual("Distributions", values = c("blue", "red")) +
  scale_y_continuous(name = "Density") +   
  scale_x_continuous(name = "Sample Means", breaks = seq(2, 8, .5), limits=c(2, 8))