Counting the number of weekly crimes

The Denver crime dataset is huge, with over 460,000 rows each marked with a reported date. Counting the number of weekly crimes is one of many queries that can be answered by grouping according to some period of time. The .resample method provides an easy interface to grouping by any possible span of time.

In this recipe, we will use both the .resample and .groupby methods to count the number of weekly crimes.

How to do it…

1. Read in the crime hdf5 dataset, set the index as the REPORTED_DATE, and then sort it to increase performance for the rest of the recipe:

   >>> crime_sort = (pd.read_hdf('data/crime.h5', 'crime') 
   ...     .set_index('REPORTED_DATE') 
   ...     .sort_index()
   ... )
   

2. To count the number of crimes per week, we need to form a group for each week. The .resample method takes a DateOffset object or alias and returns an object ready to perform an action...