Practical Data Science Cookbook - Second Edition

How to do it...

We will dive into the analysis stage with the following steps:

1. Let's start by looking at whether there is an overall trend of how mpg changes over time on average. We first want to group the data by year:

In [17]: grouped = vehicles.groupby("year") 

2. Next, we want to compute the mean of three separate columns by the previous grouping:

In [18]: averaged = grouped['comb08', 'highway08','city08'].agg([np.mean]) 

This produces a new data frame with three columns containing the mean of comb08, highway08, and city08 variables, respectively. Notice that we are using the mean function supplied by NumPy (np).

3. To make life easier, we will rename the columns and then create a new column named year, which contains the data frame's ...