# Adding Measures of Central Tendency to Histograms in R

October 4, 2012
By

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

Building on the basic histogram with a density plot, we can add measures of central tendency (in this case, mean and median) and a legend.

Like last time, we’ll use the beaver data from the datasets package.

`hist(beaver1\$temp, # histogram col = "peachpuff", # column color border = "black",  prob = TRUE, # show densities instead of frequencies xlim = c(36,38.5), ylim = c(0,3), xlab = "Temperature", main = "Beaver #1")lines(density(beaver1\$temp), # density plot lwd = 2, # thickness of line col = "chocolate3")`

Next we’ll add a line for the mean:

`abline(v = mean(beaver1\$temp), col = "royalblue", lwd = 2)`

And a line for the median:

`abline(v = median(beaver1\$temp), col = "red", lwd = 2)`

And then we can also add a legend, so it will be easy to tell which line is which.

`legend(x = "topright", # location of legend within plot area c("Density plot", "Mean", "Median"), col = c("chocolate3", "royalblue", "red"), lwd = c(2, 2, 2))`

All of this together gives us the following graphic:

In this example, the mean and median are very close, as we can see by using median() and mode().

`> mean(beaver1\$temp) 36.86219`
`> median(beaver1\$temp) 36.87`

We can do like we did in the previous post and graph beaver1 and beaver2 together by adding a layout line and changing the limits of x and y. The full code for this is available in a gist.

Here’s the output from that code:

R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.