来自MASS R库的延长的kde2d

Question

When I use kde2d function for two points on square (in my case 1000 x 1000 px) from MASS package I get elongated gaussians when x difference of points is very different from y difference of points:

library(MASS)
library(tibble)

par(mfrow = c(2, 1))
points_1 <- tribble(
  ~x,  ~y,
  100, 800,
  150, 500
) # x2-x1 = 50; y2-y1 = -300

kde_1 <- kde2d(points_1$x, points_1$y, n = 50, lims = c(1, 1000, 1, 1000))

image(kde_1)

points_2 <- tribble(
  ~x,  ~y,
  100, 800,
  650, 700
) # x2-x1 = 550; y2-y1 = -100

kde_2 <- kde2d(points_2$x, points_2$y, n = 50, lims = c(1, 1000, 1, 1000))

image(kde_2)

How to obtain round kde2d for two pints? I need something like this:

Answer 1

As the help page for kde2d says, it will use the function bandwidth.nrd to compute the bandwidth in each coordinate. You want those to be the same, so specify the h value as a scalar:

h <- mean(bandwidth.nrd(points_1$x), bandwidth.nrd(points_1$y))
kde_3 <- kde2d(points_1$x, points_1$y, h = h, n = 50, lims = c(1, 1000, 1, 1000))
image(kde_3)

which gives me

You might want a larger value for h , eg using max instead of mean :