使用 `fields::interp.surface` 从网格插值到不规则点

Question

我正在尝试从网格到一组不规则点进行双线性插值，与How can I get the value of a kernel density estimate at specific points? 相同。但是，当我尝试接受的答案时，出现尺寸不匹配错误：

n <- 100
x <- rnorm(n)
y <- 3 + 2* x * rexp(n) + rnorm(n)
# add some outliers
y[sample(1:n,20)] <- rnorm(20,20,20)
DF <- data.frame(x,y)

# Calculate 2d density over a grid
library(MASS)
dens <- kde2d(x,y)

# create a new data frame of that 2d density grid
# (needs checking that I haven't stuffed up the order here of z?)
gr <- data.frame(with(dens, expand.grid(x,y)), as.vector(dens$z))
names(gr) <- c("x", "y", "z")
newdata=data.frame(xgr=x, ygr=y)
dens <- fields::interp.surface(gr, newdata)

# the interp.surface output is 2x as long as dim(newdata)[1]
length(dens)
dim(newdata)[1]

任何帮助表示赞赏，如果这是微不足道的，我们深表歉意！

Answer 1

无需创建gr 对象。只需将dens 直接传递给interp.surface：

newdata=data.frame(x=x, y=y)
newdata$z <- fields::interp.surface(dens, newdata)