Question

我运行示例代码以生成描述马尔可夫链蒙特卡罗的图形。 https://github.com/davharris/mcmc-tutorial 但是，我遇到了最后一行代码抛出的以下异常。 “错误：美学必须是长度1或与数据相同（250000）：x，y”

代码已在下面列出。

library(MASS)
library(ggplot2)
lik = function(x, y) {
    dnorm(x - 3) * dnorm(y - x + 2)
}

grid.values = seq(min.x, max.x, length = 500)
grid = expand.grid(x = grid.values, y = grid.values)
z = lik(grid$x, grid$y)

gaussian.plot = ggplot(data = grid, aes(x = x, y = y)) + geom_raster(aes(fill = z)) + scale_fill_gradient2() + coord_equal()

gaussian.plot

maxit = 50

samples = matrix(NA, nrow = maxit, ncol = 2, dimnames = list(NULL, c("x", "y")))
samples[1, ] = c(0, 0)  # start at 0,0

for (i in 2:maxit) {

    # propose a new sample point
    proposal = samples[i - 1, ] + rnorm(2, mean = 0, sd = 1)

    # Compare its likelihood with the current position
    old.lik = lik(samples[i - 1, "x"], samples[i - 1, "y"])
    new.lik = lik(proposal["x"], proposal["y"])

    ratio = new.lik/old.lik

    # flip a coin and accept the new proposal with probability min(ratio, 1)
    if (rbinom(1, size = 1, prob = min(ratio, 1))) {
        samples[i, ] = proposal
    } else {
        # If you don't accept the proposal, just keep what you had in the     last
        # time step
        samples[i, ] = samples[i - 1, ]
    }

}


gaussian.plot + geom_path(mapping = aes(x = samples[, "x"], y = samples[, "y"]), 
color = "orange") + geom_point(mapping = aes(x = samples[, "x"], y = samples[, 
"y"]))

Answer 1

samples是一个矩阵，将其转换为as.data.frame()的数据框，以便ggplot2可以使用它。
由于您希望的点数来自与用于顶部绘图的gaussian.plot不同的数据帧，因此您需要定义数据的来源。这应该有效：

 gaussian.plot + geom_path(data=samples,aes(x = x, y = y),color = "orange") + geom_point(data=samples,aes(x = x, y = y))

r ggplot错误：美学必须是长度1或与数据相同（250000）：

1 个答案: