Pandas: Index Hierarchy

Index Hierarchy

• Hierarchical indexing is also known as multiple indexing. The multiple index is an array of tuples where each tuple is unique.

• We can create a MultiIndex from array of arrays using from_arrays() method. For example

Python program

state = ['Maharashtra','Maharashtra','Maharashtra",

"Tamilnadu',"Tamilnadu', 'Tamilnadu', 'Gujrat', 'Gujrat','Gujrat']

city = ['Mumbai', 'Pune', 'Nasik', 'Chennai', 'Madurai', 'Puducherry', 'Ahmedabad', 'Surat', 'Vadodara']

population

= [24973000,8231000,1486053,12395000,1561129,244377,8009000,6538000,2065771]

# create array of arrays

index_array = [state, city]

# create multiindex from array

multi_index = pd.MultiIndex.from_arrays(index_array, names=['State', 'City'])

# create dataframe using multiindex

df = pd.DataFrame({'Population' :population}, index=multi_index)

print(df)

Output

Code explanation: In above code,

We have created a dataframe of state, city and population. We have chosen three states and three cities from each state to represent their population.

We have created a MultiIndex object named multi_index from two arrays: state and city.

We then created a DataFrame using the population array and assigned multi_index as its index. For better understanding just observe the above output.

Review Question

1. Explain the concept of hierarchical indexing with the help of suitable example.