Adding quantile regression lines

There is another very useful kind of regression, quantiles. Drawing them under the ggplot2 package it's not challenging; it has a whole quantile dedicated function, geom_quantile(). Drawing them using ggvis and plotly is also possible, but demands way more code.

This recipe draws 20 percent, 40 percent, 60 percent, and 80 percent quantile regression lines in a diamonds' carat versus price scatterplot. Drawing are amde using ggplot2 and plotly respectively.  

Getting ready

Quantile regressions come from the quantreg package; make sure to have it installed:

> if( !require(quantreg)){ install.packages('quantreg')}

Even ggplot2 relies on quantreg to fit quantile regressions.

How to do it...

1. Load ggplot2 and use geom_quatile() to draw quantile regression lines:

library(ggplot2)
ggplot( diamonds, aes( carat, price)) + 
  geom_point(shape = '.') +
  geom_quantile(quantiles = c(.2, .4, .6, .8), 
                colour = 'blue', size = 1) +
  ylim(0, max(diamonds$price...