Numerical Computing with Python

How it works...

In step 1, we form groups by the origin and destination airport columns and then apply the size method to the groupby object, which simply returns the total number of rows for each group. Notice that we could have passed the string size to the agg method to achieve the same result. In step 2, the total number of flights for each direction between Atlanta and Houston are selected. The Series flights_count has a MultiIndex with two levels. One way to select rows from a MultiIndex is to pass the loc indexing operator a tuple of exact level values. Here, we actually select two different rows, ('ATL', 'HOU') and ('HOU', 'ATL'). We use a list of tuples to do this correctly.

Step 3 is the most pertinent step in the recipe. We would ...