Overlay histogram with density curve

Question

I am trying to make a histogram of density values and overlay that with the curve of a density function (not the density estimate).

Using a simple standard normal example, here is some data:

x <- rnorm(1000) 

I can do:

q <- qplot( x, geom="histogram") q + stat_function( fun = dnorm ) 

but this gives the scale of the histogram in frequencies and not densities. with ..density.. I can get the proper scale on the histogram:

q <- qplot( x,..density.., geom="histogram") q 

But now this gives an error:

q + stat_function( fun = dnorm ) 

Is there something I am not seeing?

Another question, is there a way to plot the curve of a function, like curve(), but then not as layer?

Answer 1

Here you go!

# create some data to work with x = rnorm(1000);  # overlay histogram, empirical density and normal density p0 = qplot(x, geom = 'blank') +      geom_line(aes(y = ..density.., colour = 'Empirical'), stat = 'density') +     stat_function(fun = dnorm, aes(colour = 'Normal')) +                          geom_histogram(aes(y = ..density..), alpha = 0.4) +                           scale_colour_manual(name = 'Density', values = c('red', 'blue')) +    theme(legend.position = c(0.85, 0.85))  print(p0) 

Answer 2

A more bare-bones alternative to Ramnath's answer, passing the observed mean and standard deviation, and using ggplot instead of qplot:

df <- data.frame(x = rnorm(1000, 2, 2))  # overlay histogram and normal density ggplot(df, aes(x)) +   geom_histogram(aes(y = stat(density))) +   stat_function(     fun = dnorm,      args = list(mean = mean(df$x), sd = sd(df$x)),      lwd = 2,      col = 'red'   )