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Recommendation system

Billions of users use various social media daily and see a lot of new suggestions there. The content includes text, images, videos, and so on depending on the social platform. Do you know how that content is suggested? 

We will learn about it in this blog.

Social media recommendation system: 

It is an algorithm that suggests relevant products to users based on a variety of factors. Sometimes, when you search for a certain product on a website you notice that you start receiving several suggestions of similar products, there is a system behind this. It is generally used to target potential users more efficiently and improve the user experience by suggesting new items, saving users’ time, and narrowing down the set of choices. 


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Watch the video to see what a recommendation system is and how it is used in various real-world applications. 


Introduction to Recommender Systems 



Now that we know the concept, let’s dive deeper into a real-world application to better comprehend it. 


YouTube’s recommendation system journey

YouTube has over 800 million videos, which is about 17,810 years of continuous video watching. It is hard for a user to repeatedly search for certain sorts of videos from millions of videos. This problem is solved by recommendation systems, which provide relevant videos based on what you are currently watching.

The system also works when you open YouTube’s home page and do not watch any videos. In this case, it shows the mixture of the subscribed, most up-to-date, promoted, and most recently watched videos.  

Let’s discuss the journey of the recommendation system on YouTube. 

In 2008, YouTube’s recommendation system ranked videos based on popularity. The issue with this approach was sometimes violent or racy videos get popular. To avoid this, YouTube built classifiers to identify this type of content and avoid recommending them. After a couple of years, YouTube started to incorporate video watch time in its recommendation system.

The reason for this was that users often watched different types of videos and there were different recommendations for them. Later, YouTube took surveys where users rated the watched videos and answered the questions upon giving low or high stars.  

Soon, YouTube’s management realized that everyone did not fill out the survey. So, YouTube trained a machine learning model on completed surveys and predicted the survey responses. YouTube did not stop there; they started to consider the likes/dislikes and share information to make the recommender system better.  

Nowadays, they are also using classifiers to identify authoritative and borderline (doesn’t quite violate community) content to make a better recommender system. 


Read more about social media algorithms in this blog


Before diving deep into the technical detail, let’s first discuss common types of recommendation systems. 

Classification of recommendation system:  

Recommendation system
Recommendation system


These types of recommendation systems are widely used in industry to solve different problems. We will go through these briefly. 


1. Content-based recommendation system

 According to the user’s past behavior or explicit feedback, content-based filtering uses item features (such as keywords, categories, etc.) to suggest additional items that are similar to what they already enjoy. 

Content based recommendation system
Content based recommendation system



2. Collaborative recommendation system 

Collaborative filtering gives information based on interactions and data acquired by the system from other users. It is divided into two types: memory-based, and model-based systems. 


a) Memory-based system 

This mechanism is further classified as user-based and item-based filtering. In the user-based approach, recommendations are made based on the user’s preferences that are similar to the preferences of other users. In the item-based approach, recommendations are made based on items similar to other items the active user likes. 


Let’s see the below illustration to understand the difference:  

User-based recommendation system
User-based and item-based recommendation system


b) Model-based system 

This mechanism provides recommendations by developing machine learning models from users’ ratings. A few commonly used machine learning models are clustering-based, matrix factorization-based, and deep learning models.  

Model-based system
Model-based system

2. Demographic-based recommendation system 

This system provides recommendations based on user demographic attributes, such as age, sex, and location. This system uses demographic information, such as a user’s age, gender, and location, to provide personalized recommendations. This type of system uses data about a user’s characteristics to suggest items that may be of particular interest to them.

For example, a recommendation system might use a user’s age and location to suggest events or activities in the user’s area that might be of interest to someone in their age group.



3. Knowledge-based recommendation system 

This system offers recommendations based on queries made by the user rather than a user’s rating history. Shortly, it is based on explicit knowledge of the item variety, user preference and suggestion criteria. This strategy is suited for complex domains where products are not acquired frequently, such as houses and automobiles. 


4. Community-based recommendation system 

This system provides recommendations based on user-interacted items within a community that shares a common interest. A community-based recommendation system is a tool that uses the interactions and preferences of a group of people with a shared interest to provide personalized recommendations to individual users.

This type of system takes into account the collective experiences and opinions of the community in order to provide personalized recommendations.


5. Hybrid recommendation system 

This system is a combination of two or more discussed recommendation systems such as content-based, collaborative-based, and so on. Sometimes a single recommendation system cannot solve an issue, thus we must combine two or more recommendation systems. 

We now have a high-level understanding of the various recommendation systems. Recall the YouTube discussion, what do you think, which recommendation method suits YouTube the most. 


It is a memory-based collaborative recommendation system. YouTube can use an item-based approach to suggest videos based on other similar videos using users’ ratings (clicked on and watched videos). To determine the most similar match, we can use matrix factorization. This is a class of collaborative recommendation systems to find the relationship between items’ and users’ entities. However, this approach has numerous limitations, such as  

  • Not being suitable for complex relations in the users and items 
  • Always recommend popular items 
  • Cold start problem (cannot anticipate items and users that we have never encountered in training data) 
  • Can only use limited information (only user IDs and item IDs)  

To address the shortcomings of the matrix factorization method, deep neural networks are designed and used by YouTube. Deep learning is based on artificial neural networks, which enable computers to comprehend and make decisions in the same way that the human brain does.

Let’s watch the video below to gain a better understanding of deep learning.



YouTube uses the deep learning model for its video recommendation system. They provide users’ watch history and context to the deep neural network. The network then learns from the provided data and uses the softmax classifier (used for multiclass classification) to differentiate among the videos. This model provides hundreds of videos from a pool of over 800 million videos. This procedure was named “candidate generation” by YouTube.  

But we just need to reveal a few of them to a certain user. So, YouTube created a ranking system in which they provide a rank (score) to each of a few hundred videos. They used the same deep learning model that assigns a score to each video for this. The score may be based on the video that the user watched from any channel and/or the most recently watched video topic.

User history and context
User history and context – Source 


We studied different recommendation systems that can be used to address various real-world challenges. These systems help to connect people with resources and information that may not have been easily discoverable otherwise, making them a useful tool for solving these challenges.

We discussed the journey of YouTube’s recommendation system, a collaborative system used by YouTube, and examined how YouTube performed well using deep learning in their systems.  

January 2, 2023

This blog will cover how to build a recommendation system using Python libraries to perform web scrapping and carry out text transformation. It will teach you how to create your own dataset and further build a content-based recommendation system.


recommendation system flowchart
A simple recommender system flow

The purpose of Data Science (DS) and Artificial Intelligence (AI) is to add value to a business by utilizing data and applying applicable programming skills. In recent years, Netflix, Amazon, Uber Eats, and other companies have made it possible for people to avail certain commodities with only a few clicks while sitting at home. However, in order to provide users with the most authentic experience possible, these platforms have developed recommendation systems that provide users with a variety of options based on their interests and preferences.

In general, recommendation systems are algorithms that curate data and provide consumers with appropriate material. There are three main types of recommendation engines

  1. Collaborative filtering: Collaborative filtering collects data regarding user behavior, activities, and preferences to predict what a person will like, based on their similarity to other users.
  1.  Content-based filtering: This algorithms analyze the possibility of objects being related to each other using statistics, and then offers possible outcomes to the user based on the highest probabilities.
  1. Hybrid of the two. In a hybrid recommendation engine, natural language processing tags can be generated for each product or item (movie, song), and vector equations are used to calculate the similarity of products.

Building a recommendation system using Python

In this blog, we will walk through the process of scraping a web page for data and using it to develop a recommendation system, using built-in python libraries. Scraping the website to extract useful data will be the first component of the blog. Moving on, text transformation will be performed to alter the extracted data and make it appropriate for our recommendation system to use.

Finally, our content-based recommender system will calculate the cosine similarity of each blog with the rest of the blogs and then suggest three comparable blogs for each blog post.

recommendation system steps
Flow for recommendation system using web scrapping

First step: Web scrapping

The purpose of going through the web scrapping process is to teach how to automate data entry for a recommender system. Knowing how to extract data from the internet will allow you to develop skills to create your own dataset using an entire webpage. Now, let us perform web scraping on the blogs page of online.datasciencedojo.com.

In this blog, we will extract relevant information to make up our dataset. From the first page, we will extract the URL, name, and description of each blog. By extracting the URL, we will have access to redirect our algorithm to each blog page and extract the name and description from the metadata.

The code below uses multiple python libraries and extracts all the URLs from the first page. In this case, it will return ten URLs. For building better concepts regarding web scrapping, I would suggest exploring and playing with these libraries to better understand their functionalities.

Note: The for loop is used to extract URLs from multiple pages.

import requests
import lxml.html
from lxml import objectify
from bs4 import BeautifulSoup
#List for storing urls
urls_final = []
#Extract the metadata of the page
for i in range(1):
url = 'https://online.datasciencedojo.com/blogs/?blogpage='+str(i)
reqs = requests.get(url)
soup = BeautifulSoup(reqs.text, 'lxml')
#Temporary lists for storing temporary data
urls_temp_1 = []
#From the metadata, get the relevant information.
for h in soup.find_all('a'):
a = h.get('href')
for i in urls_temp_1:
if i != None :
if 'blogs' in i:
if 'blogpage' in i:
if 'auth' in i:
[temp.append(x) for x in urls_temp_2 if x not in temp]
for i in temp:
if i=='https://online.datasciencedojo.com/blogs/':

Once we have the URLs, we move towards processing the metadata of each blog for extracting their name and description.

#Getting the name and description
#Now use each url to get the metadata of each blog post
for j in urls_final:
url = j
response = requests.get(url)
soup = BeautifulSoup(response.text)
#Extract the name and description from each blog
metas = soup.find_all('meta')
name.append([ meta.attrs['content'] for meta in metas if 'property' in meta.attrs and meta.attrs['property'] == 'og:title' ])
descrip_temp.append([ meta.attrs['content'] for meta in metas if 'name' in meta.attrs and meta.attrs['name'] == 'description' ])
['RegEx 101 - beginner’s guide to understand regular expressions']
['A regular expression is a sequence of characters that specifies a search pattern in a text. Learn more about Its common uses in this regex 101 guide.']

Second step: Text transformation

Similar to any task involving text, exploratory data analysis (EDA) is a fundamental part of any algorithm. In order to prepare data for our recommender system, data must be cleaned and transformed. For this purpose, we will be using built-in python libraries to remove stop words and transform data.

The code below uses the regex library to perform text transformation by removing punctuations, emojis, and more. Furthermore, we have imported a natural language toolkit (nlkt) to remove stop words.

Note: Stop words are a set of commonly used words in a language. Examples of stop words in English are “a”, “the”, “is”, “are” etc. They are so frequently used in the text that they hold a minimal amount of useful information.

import nltk
from nltk.corpus import stopwords
import re
#Removing stop words and cleaning data
stop_words = set(stopwords.words("english"))
for i in descrip_temp:
for j in i:
text = re.sub("@\S+", "", j)
text = re.sub(r'[^\w\s]', '', text)
text = re.sub("\$", "", text)
text = re.sub("@\S+", "", text)
text = text.lower()

Following this, we will be creating a bag of words. If you are not familiar with it, a bag of words is a representation of text that describes the occurrence of words within a document. It involves two things: A vocabulary of known words, and a measure of the presence of those words. For our data, it will represent all the keywords words in the dataset and calculate which words are used in each blog and the number of occurrences they have. The code below uses a built-in function to extract keywords.

from keras.preprocessing.text import Tokenizer
#Building BOW
model = Tokenizer()
bow = model.texts_to_matrix(descrip, mode='count')
bow_keys=f'Key : {list(model.word_index.keys())}'

For building better concepts, here are all the extracted keywords.

"Key : ['data', 'analytics', 'science', 'hr', 'azure', 'use', 'analysis', 'dojo',
'launched', 'offering', 'marketplace', 'learn', 'libraries', 'article', 'machine', 'learning', 'work', 'trend', 'insights', 'step',
'help', 'set', 'content', 'creators', 'webmasters', 'regular', 'expression', 'sequence', 'characters', 'specifies', 'search', 'pattern',
'text', 'common', 'uses', 'regex', '101', 'guide', 'blog', 'covers', '6', 'famous', 'python', 'easy', 'extensive', 'documentation',
'perform', 'computations', 'faster', 'enlists', 'quotes', 'analogy', 'importance', 'adoption', 'wrangling', 'privacy', 'security', 'future',
'find', 'start', 'journey', 'kinds', 'projects', 'along', 'way', 'succeed', 'complex', 'field', 'classification', 'regression', 'tree',
'applied', 'companys', 'great', 'resignation', 'era', 'economic', 'triggered', 'covid19', 'pandemic', 'changed', 'relationship', 'offices',
'workers', 'explains', 'overcoming', 'refers', 'collection', 'employee', 'reporting', 'actionable', 'click', 'code', 'explanation', 'jupyter',
'hub', 'preinstalled', 'exploration', 'modeling', 'instead', 'loading', 'clients', 'bullet', 'points', 'longwinded', 'firms',
'visualization', 'tools', 'illustrate', 'message', 'prometheus', 'powerful', 'monitoring', 'alert', 'system', 'artificial', 'intelligence',
'added', 'ease', 'job', 'wonder', 'us', 'introducing', 'different', 'inventions', 'ai', 'helping', 'grafanas', 'harvest', 'leverages', 'power',
'microsoft', 'services', 'visualize', 'query', 'alerts', 'promoting', 'teamwork', 'transparency']"

The code below assigns each keyword an index value and calculates the frequency of each word being used per blog. When building a recommendation system, these keywords and their frequencies for each blog will act as the input. Based on similar keywords, our algorithm will link blog posts together into similar categories. In this case, we will have 10 blogs converted into rows and 139 keywords converted into columns.

import pandas as pd
#Creating df
df_name.rename(columns = {0:'Blog'}, inplace = True)
result=result.drop([0], axis=1)
for i in range(len(bow)):
result.rename(columns = {i+1:i}, inplace = True)
recommendation system input
Input for recommendation system

Third step: Cosine similarity

Whenever we are performing some tasks involving natural language processing and want to estimate the similarity between texts, we use some pre-defined metrics that are famous for providing numerical evaluations for this purpose. These metrics include:

  • Euclidean Distance
  • Cosine similarity
  • Jaccard similarity
  • Pearson similarity

While all four of them can be used to evaluate a similarity index between text documents, we will be using cosine similarity for our task. Cosine similarity, in data analysis, measures the similarity between two vectors of an inner product space. It is often used to measure document similarity in text analysis.It measures the cosine of the angle between two vectors and determines a numerical value indicating the probability of those vectors being in the same direction. The code alongside the heatmap shown below visualizes the cosine similarity index for all the blogs.

from sklearn.metrics.pairwise import cosine_similarity
import seaborn as sns
#Calculating cosine similarity
sim_df = pd.DataFrame(cosine_similarity(result, dense_output=True))
for i in range(len(name)):
sim_df.rename(columns = {i:temp_df[i]},index={i:temp_df[i]}, inplace = True)
ax = sns.heatmap(sim_df)
recommendation system heatmap output
Recommendation System Heatmap Output

Fourth step: Evaluation

In the code below, our recommender system will extract the three most similar blogs for each blog using Pandas DataFrame.

Note: For each blog, the blog itself is also recommended because it was calculated to be the most similar blog, with the maximum cosine similarity index, 1.

content based recommendation system python ouput
Output for content-based recommendation System Python


This blog post covered a beginner’s method of building a recommendation system using python. While there are other methods to develop recommender systems, the first step is to outline the requirements of the task at hand. To learn more about this, experiment with the code and try to extract data from another web page or enroll in our Python for Data Science course and learn all the required concepts regarding Python fundamentals.

Full Code Available

August 17, 2022

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