DataFrames can be summarized using the groupby method. In this article we'll give you an example of how to use the groupby method.

Related Course: Data Analysis with Python and Pandas

Pandas groupby Start by importing pandas, numpy and creating a data frame. Our data frame contains simple tabular data:

In code the same table is:

import pandas as pd
import numpy as np
df1 = pd.DataFrame( { 
    "Name" : ["Alice", "Ada", "Mallory", "Mallory", "Billy" , "Mallory"] , 
    "City" : ["Sydney", "Sydney", "Paris", "Sydney", "Sydney", "Paris"]} )

We can then summarize the data using the groupby method:

print df1.groupby(["City"])[['Name']].count()

This will count the frequency of each city and return a new data frame:

The total code being:

import pandas as pd
import numpy as np
df1 = pd.DataFrame( { 
    "Name" : ["Alice", "Ada", "Mallory", "Mallory", "Billy" , "Mallory"] , 
    "City" : ["Sydney", "Sydney", "Paris", "Sydney", "Sydney", "Paris"]} )
df2 = df1.groupby(["City"])[['Name']].count()
print(df2)