Stanford Open Policing Project dataset

Analyzing Police Activity with pandas

Kevin Markham

Founder, Data School

Introduction to the dataset

Traffic stops by police officers

Stanford Open Policing Project map

Download data for any state: https://openpolicing.stanford.edu/

Preparing the data

Examine the data
Clean the data

import pandas as pd
ri = pd.read_csv('police.csv')
ri.head(3)

  state   stop_date stop_time  county_name driver_gender driver_race
0    RI  2005-01-04     12:55          NaN             M       White
1    RI  2005-01-23     23:15          NaN             M       White
2    RI  2005-02-17     04:15          NaN             M       White

Each row represents one traffic stop
NaN indicates a missing value

Locating missing values (1)

ri.isnull()

   state stop_date stop_time county_name driver_gender
0  False     False     False        True         False       
1  False     False     False        True         False       
2  False     False     False        True         False       
...

Locating missing values (2)

ri.isnull().sum()

state                     0
stop_date                 0
stop_time                 0
county_name           91741
driver_gender          5205
...

.sum() calculates the sum of each column
True = 1, False = 0

Dropping a column

ri.isnull().sum()

state                     0
stop_date                 0
stop_time                 0
county_name           91741
driver_gender          5205
driver_race            5202
...

ri.shape

(91741, 15)

county_name column only contains missing values
Drop county_name using the .drop() method

ri.drop('county_name', 
  axis='columns', inplace=True)

Dropping rows

.dropna(): Drop rows based on the presence of missing values

ri.head()

  state   stop_date stop_time driver_gender driver_race
0    RI  2005-01-04     12:55             M       White
1    RI  2005-01-23     23:15             M       White
2    RI  2005-02-17     04:15             M       White
3    RI  2005-02-20     17:15             M       White
4    RI  2005-02-24     01:20             F       White

ri.dropna(subset=['stop_date', 'stop_time'], inplace=True)

Let's practice!

Analyzing Police Activity with pandas