Hash Tables and Hash Maps in Python

Introduction

There are numerous ways for storing and accessing data and one of the most popular methods is Hash Tables. Python has an in-built data type like a dictionary to implement hash tables. Here we are explaining how to implement hash tables and hashmaps in Python using dictionaries.

Hash tables and Hashmaps in Python

Hash tables and hashmaps are data structures used to map keys to their value pairs. It is used in functions for computing an index value that contains the elements to be inserted, removed, or searched. Hash tables are used to access data easily and faster. They store key-value pairs and the key will be generated using a hash function.

The built-in dictionary data type is used to implement a hash table or hashmap and the keys are created using a hash function. Dictionary data type contains the elements that can be ordered and changed. Consider the following example that explains how a dictionary can map employee names with their employee IDs.

Creating Dictionaries in Python

In Python, there are two ways to create a dictionary as follows

• Using curly braces – {}
• Using the dict() function

Curly Braces for Creating Dictionary

Following is the example that explains how curly braces are used to create dictionaries in Python

my_dict = {‘Grace’ : ‘001’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’}

print (my_dict)

type (my_dict)

Output

{‘Grace’ : ‘001’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’}

dict

The Dict() Function for Creating Dictionary

Following is the example that explain how dict() in-built function used for creating dictionaries in Python

new_dict = dict()

print (new_dict)

type (new_dict)

Output

{} dict

Here, an empty dictionary is created as no key_value pairs are given as a parameter to the dict() function. Follow the below method to add values to the dictionary

new_dict = dict{‘Grace’ : ‘001’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’}

print (new_dict)

type (new_dict)

Output

{‘Grace’ : ‘001’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’}

dict

Nested Dictionaries

If the dictionaries that are placed within other dictionaries are known as Nested Dictionaries.

Example

emp_details = {‘Employee’: {‘Grace’: { ‘ID’: ‘001’, ‘Salary’: 5000, ‘Position’: ‘Tech Lead’},

‘Merlyn’: {‘ID’ ‘002’, ‘Salary’: 8000, ‘Position’: ‘Project Manager’},

‘Jerry’: {‘ID’: ‘003’, ‘Salary’: 10000, ‘Position’: ‘General Manager’}}}

Operations with Hash Tables using Dictionaries

Following are the various operations that can be performed on hash tables in Python using dictionaries.

• Accessing Values
• Updating Values
• Deleting Element

Accessing Values

There are many ways to access the values of a dictionary and some of them are as follows

• Using key values
• Using functions
• Implementing the for loop

Key Values for accessing dictionary values

Key values implementation is used to access dictionary values.

Example

my_dict = {‘Grace’ : ‘001’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’}

my_dict[‘Grace’]

Output

‘001’

Functions for accessing dictionary values

Python has many in-built functions to be used for accessing dictionary values and some of them, get(), keys(), values(), and so on.

Example

my_dict = {‘Grace’ : ‘001’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’}

print(my_dict.keys())

print(my_dict.values())

print(my_dict.get(‘Grace’))

Output

dict_keys([‘Grace’, ‘Merlyn’, ‘Jerry’])

dict_keys([‘001’,’002’,’003’])

001

For loop for accessing the dictionary values

For loop in Python can be used to access the key-value pairs of dictionaries easily by iterating over them.

Example

my_dict = {‘Grace’ : ‘001’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’}

print(“All keys”)

for x in my_dict:

print(x)

print(“All values”)

for x in my_dict.values():

print(x)

print(“All keys and values”

for x, y in my_dict.items()

print (x, “:”, y)

Output

All keys

Grace

Merlyn

Jerry

All values

001

002

003

All keys and values

Grace: 001

Merlyn: 002

Jerry: 003

Updating values in Dictionaries

We can modify the dictionary as per the requirement as it is a mutable data type. If we want to update the ID of the employee named grace from ‘001’ to ‘007’ or if we want to add up the employee, they are possible in Python.

Example

my_dict = {‘Grace’ : ‘001’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’}

my_dict[‘Grace] = ‘007’ #updating the value of Grace

my_dict[‘Freddy’] = ‘004’ #adding the new key-value pair

print(my_dict)

Output

{‘Grace’: ‘007’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’, ‘Freddy’: ‘004’}

Deleting key-pair values from a dictionary

Python has some popular functions used to remove items from a dictionary and they are del(), pop(), popitem(), clear(), and so on.

Example

my_dict = {‘Grace’ : ‘007’, ‘Merlyn’ : ‘002’, ‘Jerry’: ‘003’, ‘Freddy’: ‘004’}

del my_dict[‘Grace’] #removes key-value of Grace

my_dict.pop(‘Merlyn’) #removes the value of Merlyn

my_dict.popitem() #removes the last added item

print(my_dict)

Output

{‘Jerry’: ‘003’}

Converting Dictionary into a dataframe

It is possible to convert the dictionary items into a dataframe in Python programming language using the pandas library. Check out the following example that explains how to convert them into a dataframe.
Example
import pandas as pan
emp_details = {‘Employee’: {‘Grace’: { ‘ID’: ‘001’, ‘Salary’: 5000, ‘Position’: ‘Tech Lead’},
‘Merlyn’: {‘ID’ ‘002’, ‘Salary’: 8000, ‘Position’: ‘Project Manager’},
‘Jerry’: {‘ID’: ‘003’, ‘Salary’: 10000, ‘Position’: ‘General Manager’}}}
df=pd.DataFrame(emp_details[‘Employee’])
print(df)

Conclusion

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