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Joins Are No Mystery Anymore: Hands-On Tutorial — Part 2
Welcome back to the second part of our series, “Joins Are No Mystery Anymore: Hands-On Tutorial.” In the first part, we explored the foundational types of joins, including Inner Join, Left Join, Right Join, Full Join, and Semi Join. Through practical, real-life scenarios and step-by-step code examples, we learned how to effectively combine datasets and uncover valuable insights.
In this second part, we’ll delve into more advanced join techniques. We’ll start with Anti Joins, which help identify unmatched rows between datasets. Following that, we’ll explore Cross Joins, Natural Joins, Self Joins, and Equi Joins. Each join type will be demonstrated with real-life scenarios to enhance your understanding and practical application. Get ready to take your data analysis skills to the next level!
Anti Join
An Anti Join returns all rows from the left table where there are no matching values in the right table. It is useful for identifying rows in the left table that do not have corresponding rows in the right table.
Explanation of the Scenario
In this scenario, we have subscription information and payment records. We want to find subscriptions that have not been paid for. This helps in identifying outstanding payments and managing accounts receivable.
Data file:
https://github.com/kgryczan/medium_publishing/blob/main/anti_join_data.RData
Description of the Datasets
We will use two datasets:
- subscriptions: Contains information about subscriptions.
- Columns: subscription_id, customer_id, start_date
- payments: Contains information about payments made for subscriptions.
- Columns: payment_id, subscription_id, amount, payment_date
Step-by-Step Code Examples
Loading the datasets:
# Load the necessary libraries
library(dplyr)
# Load the datasets
load("anti_join_data.RData")
# Display the datasets
print(subscriptions)
# A tibble: 30 × 3
subscription_id customer_id start_date
<int> <int> <date>
1 1 108 2024-01-01
2 2 107 2024-01-02
3 3 110 2024-01-03
4 4 113 2024-01-04
5 5 110 2024-01-05
6 6 111 2024-01-06
7 7 108 2024-01-07
8 8 107 2024-01-08
9 9 107 2024-01-09
10 10 112 2024-01-10
# ℹ 20 more rows
print(payments)
payment_id subscription_id amount payment_date
<int> <int> <dbl> <date>
1 201 4 154. 2024-01-05
2 202 29 134. 2024-01-06
3 203 25 158. 2024-01-07
4 204 20 169. 2024-01-08
5 205 18 170. 2024-01-09
6 206 27 91.4 2024-01-10
7 207 23 52.4 2024-01-11
8 208 21 151. 2024-01-12
9 209 12 76.4 2024-01-13
10 210 25 133. 2024-01-14
# ℹ 20 more rowsPerforming the Anti Join
# Perform the anti join
unpaid_subscriptions <- anti_join(subscriptions, payments, by = "subscription_id")
# Display the result
print(unpaid_subscriptions)
# A tibble: 13 × 3
subscription_id customer_id start_date
<int> <int> <date>
1 1 108 2024-01-01
2 2 107 2024-01-02
3 5 110 2024-01-05
4 6 111 2024-01-06
5 8 107 2024-01-08
6 10 112 2024-01-10
7 15 113 2024-01-15
8 16 115 2024-01-16
9 19 115 2024-01-19
10 22 111 2024-01-22
11 24 108 2024-01-24
12 28 115 2024-01-28
13 30 102 2024-01-30Explanation of the Code:
- We first load the datasets using the load function.
- We then use the anti_join function from the dplyr package to filter the subscriptions dataset to include only those subscriptions that do not have matching entries in the payments dataset, based on the subscription_id column.
- Finally, we display the result to see which subscriptions have not been paid for.
Interpretation of Results
The resulting dataset unpaid_subscriptions contains only the rows from the subscriptions dataset where there is no matching row in the payments dataset. This means that only unpaid subscriptions are included.
Homework for Readers
In the same anti_join_data.RData file, there is another set of datasets for a more creative scenario. You will find:
- courses: Contains information about courses.
- Columns: course_id, course_name, instructor
- enrollments: Contains information about student enrollments.
- Columns: enrollment_id, course_id, student_id, enrollment_date
Your task is to perform an anti join on these datasets to identify courses that have no enrollments. Use the course_id column for joining.
Cross Join
A Cross Join returns the Cartesian product of two tables, combining all rows from the left table with all rows from the right table. This join type is useful when you want to create all possible combinations of the rows in two tables.
Explanation of the Scenario
In this scenario, we have menu items and days of the week. We want to create a schedule of menu items for each day of the week. This helps in planning and organizing the weekly menu offerings.
Data file:
https://github.com/kgryczan/medium_publishing/blob/main/cross_join_data.RData
Description of the Datasets
We will use two datasets:
- menu_items: Contains information about the menu items.
- Columns: item_id, item_name, category
- days_of_week: Contains information about the days of the week.
- Columns: day_id, day_name
Step-by-Step Code Examples
Loading the datasets
# Load the necessary libraries
library(dplyr)
# Load the datasets
load("cross_join_data.RData")
# Display the datasets
print(menu_items)
# A tibble: 10 × 3
item_id item_name category
<int> <chr> <chr>
1 1 Pancakes Breakfast
2 2 Sandwich Lunch
3 3 Salad Lunch
4 4 Burger Lunch
5 5 Soup Dinner
6 6 Pizza Dinner
7 7 Spaghetti Dinner
8 8 Tacos Dinner
9 9 Sushi Dinner
10 10 Steak Dinner
print(days_of_week)
# A tibble: 7 × 2
day_id day_name
<int> <chr>
1 1 Monday
2 2 Tuesday
3 3 Wednesday
4 4 Thursday
5 5 Friday
6 6 Saturday
7 7 Sunday Performing the Cross Join
# Perform the cross join
menu_schedule <- tidyr::crossing(menu_items, days_of_week)
# Display the result
print(menu_schedule)
# A tibble: 70 × 5
item_id item_name category day_id day_name
<int> <chr> <chr> <int> <chr>
1 1 Pancakes Breakfast 1 Monday
2 1 Pancakes Breakfast 2 Tuesday
3 1 Pancakes Breakfast 3 Wednesday
4 1 Pancakes Breakfast 4 Thursday
5 1 Pancakes Breakfast 5 Friday
6 1 Pancakes Breakfast 6 Saturday
7 1 Pancakes Breakfast 7 Sunday
8 2 Sandwich Lunch 1 Monday
9 2 Sandwich Lunch 2 Tuesday
10 2 Sandwich Lunch 3 Wednesday
# ℹ 60 more rowsExplanation of the Code:
- We first load the datasets using the load function.
- We then use the crossing function from the tidyr package to perform the cross join between the menu_items and days_of_week datasets. This function creates all possible combinations of the rows in the two datasets.
- Finally, we display the result to see the complete schedule of menu items for each day of the week.
Interpretation of Results
The resulting dataset menu_schedule contains all possible combinations of the rows from the menu_items and days_of_week datasets. Each row represents a menu item scheduled for a particular day of the week.
Homework for Readers
In the same cross_join_data.RData file, there is another set of datasets for a more creative scenario. You will find:
- shirts: Contains information about shirts.
- Columns: shirt_id, color, size
- pants: Contains information about pants.
- Columns: pants_id, color, size
Your task is to perform a cross join on these datasets to generate all possible outfits by combining shirts and pants. Use the shirt_id and pants_id columns for joining.
Natural Join
A Natural Join joins two tables based on columns with the same name and type in both tables. It automatically matches rows with equal values in the common columns, removing the need to specify the joining column.
Explanation of the Scenario
In this scenario, we have authors and books. We want to find authors and their corresponding books based on a common column. This helps in linking authors with the books they have written.
Data file:
https://github.com/kgryczan/medium_publishing/blob/main/natural_join_data.RData
Description of the Datasets
We will use two datasets:
- authors: Contains information about authors.
- Columns: author_id, name, nationality
- books: Contains information about books.
- Columns: book_id, author_id, title, genre
Step-by-Step Code Examples
Loading the datasets:
# Load the necessary libraries
library(dplyr)
# Load the datasets
load("natural_join_data.RData")
# Display the datasets
print(authors)
# A tibble: 20 × 3
author_id name nationality
<int> <chr> <chr>
1 1 Author A Australia
2 2 Author B Australia
3 3 Author C Canada
4 4 Author D USA
5 5 Author E UK
6 6 Author F USA
7 7 Author G Australia
8 8 Author H Australia
9 9 Author I UK
10 10 Author J Australia
11 11 Author K Australia
12 12 Author L USA
13 13 Author M USA
14 14 Author N Canada
15 15 Author O Canada
16 16 Author P Canada
17 17 Author Q USA
18 18 Author R Australia
19 19 Author S USA
20 20 Author T USA
print(books)
# A tibble: 20 × 4
book_id author_id title genre
<int> <int> <chr> <chr>
1 101 1 Book A Fantasy
2 102 2 Book B Fiction
3 103 3 Book C Sci-Fi
4 104 4 Book D Fiction
5 105 5 Book E Sci-Fi
6 106 6 Book F Fantasy
7 107 7 Book G Fantasy
8 108 8 Book H Mystery
9 109 9 Book I Mystery
10 110 10 Book J Mystery
11 111 11 Book K Fantasy
12 112 12 Book L Fiction
13 113 13 Book M Fiction
14 114 14 Book N Mystery
15 115 15 Book O Sci-Fi
16 116 16 Book P Sci-Fi
17 117 17 Book Q Fantasy
18 118 18 Book R Sci-Fi
19 119 19 Book S Mystery
20 120 20 Book T MysteryPerforming the Natural Join:
# Perform the natural join
authors_books <- authors %>%
inner_join(books, by = "author_id")
# Display the result
print(authors_books)
# A tibble: 20 × 6
author_id name nationality book_id title genre
<int> <chr> <chr> <int> <chr> <chr>
1 1 Author A Australia 101 Book A Fantasy
2 2 Author B Australia 102 Book B Fiction
3 3 Author C Canada 103 Book C Sci-Fi
4 4 Author D USA 104 Book D Fiction
5 5 Author E UK 105 Book E Sci-Fi
6 6 Author F USA 106 Book F Fantasy
7 7 Author G Australia 107 Book G Fantasy
8 8 Author H Australia 108 Book H Mystery
9 9 Author I UK 109 Book I Mystery
10 10 Author J Australia 110 Book J Mystery
11 11 Author K Australia 111 Book K Fantasy
12 12 Author L USA 112 Book L Fiction
13 13 Author M USA 113 Book M Fiction
14 14 Author N Canada 114 Book N Mystery
15 15 Author O Canada 115 Book O Sci-Fi
16 16 Author P Canada 116 Book P Sci-Fi
17 17 Author Q USA 117 Book Q Fantasy
18 18 Author R Australia 118 Book R Sci-Fi
19 19 Author S USA 119 Book S Mystery
20 20 Author T USA 120 Book T MysteryExplanation of the Code:
- We first load the datasets using the load function.
- We then use the inner_join function from the dplyr package to perform the natural join between the authors and books datasets on the author_id column.
- Finally, we display the result to see which authors have written which books.
Interpretation of Results
The resulting dataset authors_books contains all rows from both the authors and books datasets where there is a matching value in the author_id column. This means that only authors who have written books are included, along with the details of those books. (Yes, it is a kind of inner join.)
Homework for Readers
In the same natural_join_data.RData file, there is another set of datasets for a more creative scenario. You will find:
- staff: Contains information about staff members.
- Columns: staff_id, name, role
- assignments: Contains information about project assignments.
- Columns: assignment_id, staff_id, project_name
Your task is to perform a natural join on these datasets to combine staff details with their project assignments. Use the staff_id column for joining.
Self Join
A Self Join is a join of a table to itself. It is used to compare rows within the same table. This can be particularly useful for hierarchical data, such as organizational structures, where you need to find relationships between rows within the same table.
Explanation of the Scenario
In this scenario, we have employee information, and each employee has a manager, who is also an employee. We want to find the relationship between employees and their managers using the same table. This helps in understanding the organizational hierarchy.
Data file:
https://github.com/kgryczan/medium_publishing/blob/main/self_join_data.RData
Description of the Datasets
We will use one dataset:
- employees: Contains information about employees and their managers.
- Columns: employee_id, name, manager_id
Step-by-Step Code Examples
Loading the dataset
# Load the necessary libraries
library(dplyr)
# Load the dataset
load("self_join_data.RData")
# Display the dataset
print(employees)
# A tibble: 20 × 3
employee_id name manager_id
<int> <chr> <int>
1 1 Alice E 12
2 2 Bob C 6
3 3 Carol L 8
4 4 Zoe K 15
5 5 Alice G 10
6 6 Bob D 7
7 7 Carol S 19
8 8 Zoe T 1
9 9 Alice O 13
10 10 Bob O 2
11 11 Carol G 16
12 12 Zoe P 8
13 13 Alice H 4
14 14 Bob K 14
15 15 Carol B 18
16 16 Zoe E 4
17 17 Alice O 7
18 18 Bob T 14
19 19 Carol R 8
20 20 Zoe G 16Performing the Self Join
# Perform the self join
employees_managers <- employees %>%
inner_join(employees, by = c("manager_id" = "employee_id"), suffix = c("_employee", "_manager"))
# Display the result
print(employees_managers)
# A tibble: 20 × 5
employee_id name_employee manager_id name_manager manager_id_manager
<int> <chr> <int> <chr> <int>
1 1 Alice E 12 Zoe P 8
2 2 Bob C 6 Bob D 7
3 3 Carol L 8 Zoe T 1
4 4 Zoe K 15 Carol B 18
5 5 Alice G 10 Bob O 2
6 6 Bob D 7 Carol S 19
7 7 Carol S 19 Carol R 8
8 8 Zoe T 1 Alice E 12
9 9 Alice O 13 Alice H 4
10 10 Bob O 2 Bob C 6
11 11 Carol G 16 Zoe E 4
12 12 Zoe P 8 Zoe T 1
13 13 Alice H 4 Zoe K 15
14 14 Bob K 14 Bob K 14
15 15 Carol B 18 Bob T 14
16 16 Zoe E 4 Zoe K 15
17 17 Alice O 7 Carol S 19
18 18 Bob T 14 Bob K 14
19 19 Carol R 8 Zoe T 1
20 20 Zoe G 16 Zoe E 4Explanation of the Code:
- We first load the dataset using the load function.
- We then use the inner_join function from the dplyr package to join the employees table to itself. The join condition matches the manager_id of one row with the employee_id of another row. The suffix argument is used to distinguish between the employee and manager columns.
- Finally, we display the result to see the relationship between employees and their managers.
Interpretation of Results
The resulting dataset employees_managers contains pairs of employees and their managers. Each row shows an employee along with their corresponding manager, including details such as names and IDs.
Homework for Readers
In the same self_join_data.RData file, there is another set of datasets for a more creative scenario. You will find:
- friends: Contains information about friendships within a social network.
- Columns: person_id, friend_id
Your task is to perform a self join on this dataset to analyze the friendships and find mutual friends. Use the person_id and friend_id columns for joining.
Equi Join
An Equi Join is a type of join that combines rows from two tables based on equality conditions between specified columns. It is one of the most common types of joins used in SQL and relational database management. Take into a consideration that all types we already talked about are equi joins. It is just wider definition, beacuse we are looking for equality of keys.
Explanation of the Scenario
In this scenario, we have orders and order details. We want to join these tables to get a comprehensive view of each order along with its details. This helps in understanding the full scope of each transaction.
Data file:
https://github.com/kgryczan/medium_publishing/blob/main/equi_join_data.RData
Description of the Datasets
We will use two datasets:
- orders: Contains information about customer orders.
- Columns: order_id, customer_id, order_date
- order_details: Contains detailed information about each order.
- Columns: order_detail_id, order_id, product_id, quantity
Step-by-Step Code Examples
Loading the datasets
# Load the necessary libraries
library(dplyr)
# Load the datasets
load("equi_join_data.RData")
# Display the datasets
print(orders)
# A tibble: 20 × 3
order_id customer_id order_date
<int> <int> <date>
1 1 113 2024-01-01
2 2 113 2024-01-02
3 3 112 2024-01-03
4 4 105 2024-01-04
5 5 117 2024-01-05
6 6 115 2024-01-06
7 7 112 2024-01-07
8 8 107 2024-01-08
9 9 117 2024-01-09
10 10 106 2024-01-10
11 11 105 2024-01-11
12 12 109 2024-01-12
13 13 117 2024-01-13
14 14 113 2024-01-14
15 15 101 2024-01-15
16 16 107 2024-01-16
17 17 115 2024-01-17
18 18 103 2024-01-18
19 19 108 2024-01-19
20 20 115 2024-01-20
print(order_details)
# A tibble: 40 × 4
order_detail_id order_id product_id quantity
<int> <int> <int> <int>
1 1 17 206 10
2 2 18 215 4
3 3 13 218 8
4 4 16 217 3
5 5 2 217 5
6 6 2 203 4
7 7 20 219 9
8 8 18 214 4
9 9 12 218 4
10 10 14 214 4
# ℹ 30 more rowsPerforming the Equi Join
# Perform the equi join
orders_with_details <- inner_join(orders, order_details, by = "order_id")
# Display the result
print(orders_with_details)
# A tibble: 40 × 6
order_id customer_id order_date order_detail_id product_id quantity
<int> <int> <date> <int> <int> <int>
1 1 113 2024-01-01 39 210 5
2 2 113 2024-01-02 5 217 5
3 2 113 2024-01-02 6 203 4
4 2 113 2024-01-02 22 219 1
5 2 113 2024-01-02 25 220 8
6 2 113 2024-01-02 36 213 3
7 2 113 2024-01-02 38 202 9
8 4 105 2024-01-04 12 215 4
9 4 105 2024-01-04 24 201 5
10 4 105 2024-01-04 30 219 3
# ℹ 30 more rowsExplanation of the Code:
- We first load the datasets using the load function.
- We then use the inner_join function from the dplyr package to perform the equi join between the orders and order_details datasets on the order_id column.
- Finally, we display the result to see the full details of each order.
Interpretation of Results
The resulting dataset orders_with_details contains all rows from the orders dataset with the matching rows from the order_details dataset based on the order_id column. This means that each order is enriched with its detailed information.
Homework for Readers
In the same equi_join_data.RData file, there is another set of datasets for a more creative scenario. You will find:
- athletes: Contains information about athletes.
- Columns: athlete_id, name, sport
- performance_records: Contains information about performance records of athletes.
- Columns: record_id, athlete_id, event, score
Your task is to perform an equi join on these datasets to match athletes with their performance records. Use the athlete_id column for joining.
In this second part of our series, “Joins Are No Mystery Anymore: Hands-On Tutorial,” we delved into more advanced join techniques that are essential for comprehensive data analysis. We explored:
- Anti Join: Identifying rows in one table that do not have corresponding rows in another, helping to spot outstanding payments.
- Cross Join: Creating all possible combinations of rows from two tables, useful for planning and organizing.
- Natural Join: Automatically joining tables based on columns with the same names and types, simplifying the linking process.
- Self Join: Comparing rows within the same table to uncover relationships, such as employee-manager hierarchies.
- Equi Join: Combining rows from two tables based on equality conditions, providing detailed insights into orders and their specifics.
Through practical scenarios and step-by-step code examples, we enhanced our understanding of these joins and their applications. Each join type was demonstrated with real-life datasets, allowing you to see how these techniques can be applied to solve everyday data problems.
Next week, we will conclude our series with even more specialized join techniques. We’ll cover Non-Equi Joins, Rolling Joins, Overlap Joins, and Fuzzy Joins. These advanced joins will help you handle more complex data scenarios, such as matching based on non-equality conditions, finding the nearest matches, and dealing with approximate or fuzzy data. Stay tuned as we unlock the full potential of joins in R and take your data analysis skills to the ultimate level.
Thank you for sticking with us through the second part of our “Joins Are No Mystery Anymore: Hands-On Tutorial” series! Your dedication to mastering data joins in R is commendable.
As a special treat for our patient readers, next week we’ll dive into “Anatomy of a Basic Joining Function.” This extra content will break down the different arguments in joining functions, explaining what each one does and how it changes the output. It’s a deep dive into the mechanics of joins that will enhance your understanding and give you even greater control over your data analysis.
Stay tuned and happy coding!
Joins Are No Mystery Anymore: Hands-On Tutorial — Part 2 was originally published in Numbers around us on Medium, where people are continuing the conversation by highlighting and responding to this story.
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