在R中绘制核密度函数点不成功的点

Question

I'm trying to get some points on my density plot for the seq(-3, 3) [ie, 7 numbers]. I get the 7 corresponding density values but when I try to execute points , I get:

Error in xy.coords(x, y) : 'x' and 'y' lengths differ

As really there is no length difference, I assume there is class() difference problem between x, and y for points() . I appreciate a solution?

Here is the R code:

positions = rnorm(1e4)

DENS = density(positions, adjust = 2, n = 1e4)

x.DENS = DENS$x
y.DENS = DENS$y

plot( DENS, col = "red", lwd = 3, xlab = "Positions",
  ylab = "Density", xlim = c(-6, 6), main = 
  NA, bty = 'n', zero.line = F)

x.DENS.2 = seq(-3, 3)
y.DENS.2 = approx(x.DENS, y.DENS, xout = x.DENS.2 ) ## get the x.DENS.2 density values

points(x.DENS.2, y.DENS.2) ## Error 

Answer 1

The y.DENS.2 -object is actually a list with x and y components:

str(y.DENS.2 )
List of 2
 $ x: int [1:7] -3 -2 -1 0 1 2 3
 $ y: num [1:7] 0.00514 0.0642 0.23952 0.37896 0.24057 ...

... so you can just use

points(y.DENS.2, col="blue")

Answer 2

The last line is incorrect. Please change it to

points(x.DENS.2, y.DENS.2$y)

Here is the full codes. It works on my side. So, when you plot the results, it will be very helpful to check the dimension of your inputs to make sure that they matched.

positions = rnorm(1e4)

DENS = density(positions, adjust = 2, n = 1e4)

x.DENS = DENS$x
y.DENS = DENS$y

plot( DENS, col = "red", lwd = 3, xlab = "Positions",
      ylab = "Density", xlim = c(-6, 6), main = 
        NA, bty = 'n', zero.line = F)

x.DENS.2 = seq(-3, 3)
y.DENS.2 = approx(x.DENS, y.DENS, xout = x.DENS.2 ) ## get the x.DENS.2 density values

points(x.DENS.2, y.DENS.2$y)