Question

I have a density plot graphed using:

plot(density(x))

What I am interested in doing is creating a line for something like x = 5 from the x-axis to the corresponding spot on the curve.

Like this:

Answer 1

You can do this by first storing the density values in an object, and then retrieving the x and y elements from this object. In the following example I use findInterval to retrieve the y-value for the given x-value:

x <- rnorm(1000) # Sample data
y <- density(x)  # Calculate and store density

x0 <- 2 # Desired position on x-axis
y0 <- y$y[findInterval(x0, y$x)] # Corresponding y value

plot(density(x))
segments(x0, 0, x0, y0)