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Different Plot Types
Simple Bar Chart

The plt.bar function allows you to create simple bar charts to compare multiple categories of data.

Some possible data that would be displayed with a bar chart:

  • x-axis — famous buildings, y-axis — heights
  • x-axis — different planets, y-axis — number of days in the year
  • x-axis — programming languages, y-axis — lines of code written by you

You call plt.bar with two arguments:

  • the x-values — a list of x-positions for each bar
  • the y-values — a list of heights for each bar

In most cases, we will want our x-values to be a list that looks like [0, 1, 2, 3 ...] and has the same number of elements as our y-values list. We can create that list manually, but we can also use the following code:

heights = [88, 225, 365, 687, 4333, 10756, 30687, 60190, 90553] x_values = range(len(heights))

The range function creates a list of consecutive integers (i.e., [0, 1, 2, 3, ...]). It needs an argument to tell it how many numbers should be in the list. For instance, range(5) would make a list with 5 numbers. We want our list to be as long as our bar heights (heights in this example). len(heights) tell us how many elements are in the list heights.

Here is an example of how to make a bar chart using plt.bar to compare the number of days in a year on the different planets:

days_in_year = [88, 225, 365, 687, 4333, 10756, 30687, 60190, 90553] plt.bar(range(len(days_in_year)), days_in_year) plt.show()

The result of this is:

planet_bar_chart

At this point, it’s hard to tell what this represents, because it’s unclearly labeled. We’ll fix that in later sections!

In the instructions below, we’ll use plt.bar to create a chart for a fake cafe called MatplotSip. We will be comparing the sales of different beverages on a given day.

Instructions

1.

We are going to help the cafe MatplotSip analyze some of the sales data they have been collecting. In script.py, we have included a list of drink categories and a list of numbers representing the sales of each drink over the past month.

Use plt.bar to plot numbers of drinks sold on the y-axis. The x-values of the graph should just be the list [0, 1 ... , n-1], where n is the number of categories (drinks) we are plotting. So at x=0, we’ll have the number of cappuccinos sold.

2.

Show the plot and examine it. At this point, we can’t tell which bar corresponds to which drink, so this chart is not very helpful. We’ll fix this in the next section.

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