Sorting a boxplot based on median value

Question

I'd like to use R to make a series of boxplots which are sorted by median value. Suppose then I execute:

boxplot(cost ~ type) 

This would give me some boxplots were cost is shown on the y axis and the type category is visible on the x-axis:

-----     -----   |         |  [ ]        |   |        [ ]   |         | -----     -----   A         B 

However, what I'd like is the boxplot figures sorted from highest to lowest median value. My suspicion is that what I need to do is change the labels of the type (A or B) to numerically indicate which is the lowest and highest median value, but I wonder if there is a more clever way to solve the problem.

Answer 1

Check out ?reorder. The example seems to be what you want, but sorted in the opposite order. I changed -count in the first line below to sort in the order you want.

  bymedian <- with(InsectSprays, reorder(spray, -count, median))   boxplot(count ~ bymedian, data = InsectSprays,           xlab = "Type of spray", ylab = "Insect count",           main = "InsectSprays data", varwidth = TRUE,           col = "lightgray")