How to do Inner Join in R?

How to do an inner join on data frames in R? To perform inner join use either merge() function, dplyr inner_join() function, or use reduce() from tidyverse. Using the dplyr function is the best approach as it runs faster than the R base approach. dplyr package provides several functions to join data frames in R.

In R, Inner join or natural join is the default join and it’s mostly used joining data frames, it is used to join data.frames on a specified single or multiple columns, and where column values don’t match the rows get dropped from both data.frames (emp & dept).

1. Quick Examples of Inner Join

Following are quick examples of performing inner join on data frames.

# Quick Examples

# Inner join
df2 <- merge(x=emp_df,y=dept_df, 
             by="dept_id")

# Inner join on multiple columns
df2 <- merge(x=emp_df,y=dept_df, 
             by=c("dept_id","dept_branch_id"))

# Inner join on different columns
df2 <- merge(x=emp_df,y=dept_df, 
      by.x=c("dept_id","dept_branch_id"), 
      by.y=c("dept_id","dept_branch_id"))

# Load dplyr package
library(dplyr)

# Using dplyr - inner join multiple columns
df2 <- emp_df %>% inner_join( dept_df, 
           by=c('dept_id','dept_branch_id'))

# Using dplyr - inner join on different columns
df2 <- emp_df %>% inner_join( dept_df, 
        by=c('dept_id'='dept_id', 
             'dept_branch_id'='dept_branch_id'))

# Load tidyverse package
library(tidyverse)

# Inner Join  data.frames
list_df = list(emp_df,dept_df)
df2 <- list_df %>% reduce(inner_join, by='dept_id')
df2

Let’s create two Data Frames, in the below example dept_id and dept_branch_id columns exists on both emp_df and dept_df data frames.

# Create emp Data Frame
emp_df=data.frame(
  emp_id=c(1,2,3,4,5,6),
  name=c("Smith","Rose","Williams","Jones","Brown","Brown"),
  superior_emp_id=c(-1,1,1,2,2,2),
  dept_id=c(10,20,10,10,40,50),
  dept_branch_id= c(101,102,101,101,104,105)
)

# Create dept Data Frame
dept_df=data.frame(
  dept_id=c(10,20,30,40),
  dept_name=c("Finance","Marketing","Sales","IT"),
  dept_branch_id= c(101,102,103,104)
)

emp_df
dept_df

Yields below output.

2. Inner Join using merge()

R base provides a merge() function that is used to perform an inner join on two, or more data frames. This function takes x and y data frames as left and right respectively and finally specifies the by param with the column name you want to join.

The following example performs an inner join on the column dept_id on emp_df and dept_df column. Here by default, it uses all=FALSE. This join is similar to a set intersection operation.

# inner join
df2 <- merge(x=emp_df,y=dept_df, 
                by="dept_id")
df2

Yields below output. if you have the same column names that are not used in the join condition, it suffixes with the x and y to the columns on the result. In the below example check dept_branch_id.

2.1 Inner Join on Multiple Columns

To perform an inner join on multiple columns with the same names on both data frames, use all the column names as a list to by param. I have also created a dedicated article where I have explained how to perform join on multiple columns using several ways.

# Using merge with same column names
df2 <- merge(x=emp_df,y=dept_df, 
             by=c("dept_id","dept_branch_id"))
             
df2

Yields below output.

2.2 Inner Join Different Column Names

Sometimes you will have data frames with different column names and you wanted to perform an inner join on these columns, to do so specify the column names from both data frames with params by.x and by.y.

# R join multiple columns
df2 <- merge(x=emp_df,y=dept_df, 
      by.x=c("dept_id","dept_branch_id"), 
      by.y=c("dept_id","dept_branch_id"))
df2

Since our data frame has the same column names, it results in the same output as above, I have created another article where I have explained how to perform join on different column names.

3. Using dplyr to Perform Inner Join in R

Using the inner_join() function from the dplyr package is the best approach to performing the inner join on two data frames. To use dplyr, you have to install it first using install.packages(‘dplyr’) and load it using library(dplyr).

All functions in dplyr package take data.frame as a first argument. When we use dplyr package, we mostly use the infix operator %>% from magrittr, it passes the left-hand side of the operator to the first argument of the right-hand side of the operator. For example, x %>% f(y) converted into f(x, y) so the result from the left-hand side is then “piped” into the right-hand side. 

3.1 Multiple Columns with dplyr package

# Load dplyr package
library(dplyr)

# Using dplyr - inner join multiple columns
df2 <- emp_df %>% inner_join( dept_df, 
            by=c('dept_id','dept_branch_id'))
df2

Yields below output.

3.2 Using Different Column Names with dplyr package

# Load dplyr package
library(dplyr)

# join on multiple columns
df2 <- emp_df %>% inner_join( dept_df, 
        by=c('dept_id'='dept_id', 
             'dept_branch_id'='dept_branch_id'))df2

Yields the same output as above.

4. Using tidyverse Package

By using reduce() function from tidyverse package you can perform join on multiple data frames, to perform inner join use inner_join keyword.

# Load tidyverse package
library(tidyverse)

# Inner Join  data.frames
list_df = list(emp_df,dept_df)
df2 <- list_df %>% reduce(inner_join, by='dept_id')
df2

5. Conclusion

In this article, you have learned how to perform an inner join on two data frames using the R base merge() function, inner_join() functions from the dplyr package, and reduce() from the tidyverse package. Using the dplyr approach is the best to use when you are joining on larger datasets as it performs efficiently over the R base.

Related Articles

• R Join on Different Column Names
• R Semi Join
• R Anti Join
• R Outer Join
• R Right Join
• R Left Join
• R Semi Join on Two Data Frames
• Nested For Loop in R
• Break and Next (Continue) Statements in R