If we want to compare two sets of data while preserving knowledge of the total between them, we can also stack the bars instead of putting them side by side. For instance, if someone was plotting the hours they’ve spent on entertaining themselves with video games and books in the past week, and wanted to also get a feel for total hours spent on entertainment, they could create a stacked bar chart:

We do this by using the keyword bottom. The top set of bars will have bottom set to the heights of the other set of bars. So the first set of bars is plotted normally:

video_game_hours = [1, 2, 2, 1, 2]

plt.bar(range(len(video_game_hours)),
  video_game_hours) 

and the second set of bars has bottom specified:

book_hours = [2, 3, 4, 2, 1]

plt.bar(range(len(book_hours)),
  book_hours,
  bottom=video_game_hours)

This starts the book_hours bars at the heights of the video_game_hours bars. So, for example, on Monday the orange bar representing hours spent reading will start at a value of 1 instead of 0, because 1 hour was spent playing video games.

Let’s try this out with the MatplotSip data from the last exercise.