how to add a fitted distribution to a histogram

Question

i am trying to add a fitted distribution to the histogram, but after I run it, it is just a straight line. How can i get a density line? hist(data$price) lines(density(data$price)), lwd = 2, col ="red")

Answer 1

You are using graphics function hist. Use MASS function truehist instead

MASS::truehist(data$price)
lines(density(data$price)), lwd = 2, col ="red")

Answer 2

@Chriss gave a good solution--it does produce a density curve on top of the histogram; however, it changes the y-axis so that you only see the density values (losing the count values).

Here is an alternate solution that will place the frequency counts on the left-side y-axis and add density as a right-side y-axis. Tweak code as needed for things like bins, color, etc. I'm using the mtcars data as an example since there was no code or data provided in the question to replicate. In addition to the two libraries used here (ggpubr and cowplot), you may need to use some ggplot functions to better customize these plot options.

Code for this solution was modified from https://www.datanovia.com/en/blog/ggplot-histogram-with-density-curve-in-r-using-secondary-y-axis/

# packages needed
library(ggpubr)
library(cowplot)

# load data (none provided in the original question)
data("mtcars")

# create histogram (I have 10 bins here, but you may need a different amount)
phist <- gghistogram(mtcars, x="hp", bins=10, fill="blue", ylab="Count (blue)") + ggtitle("Car Horsepower Histogram")

# create density plot, removing many plot elements
pdens <- ggdensity(mtcars, x="hp", col="red", size=2, alpha = 0, ylab="Density (red)") +
scale_y_continuous(expand = expansion(mult = c(0, 0.05)), position = "right")  +
  theme_half_open(11, rel_small = 1) +
  rremove("x.axis")+
  rremove("xlab") +
  rremove("x.text") +
  rremove("x.ticks") +
  rremove("legend")

# overlay and display the plots
aligned_plots <- align_plots(phist, pdens, align="hv", axis="tblr")
ggdraw(aligned_plots[[1]]) + draw_plot(aligned_plots[[2]])