How to Do a Left Join in R?

In this article, we will discuss how to do a left join in R programming language.

A left join is used to join the table by selecting all the records from the first dataframe and only matching records in the second dataframe.

Method 1: Using merge() function

This function is used to join the dataframes based on the x parameter that specifies left join.

Syntax:

merge(dataframe1,dataframe2, all.x=TRUE)

where,

• dataframe1 is the first dataframe
• dataframe2 is the second dataframe

Example: R program to perform two dataframes and perform left join on name column

R

# create first dataframe
data1=data.frame('name'=c('siva','ramu','giri','geetha'),
                 'age'=c(21,23,21,20))

# display
print(data1)

# create second dataframe
data2=data.frame('name'=c('siva','ramya','giri','geetha','pallavi'),
                 'marks'=c(21,23,21,20,30))

# display
print(data2)

print("=========================")

# left join on name column
print(merge(data1, data2, by='name', all.x=TRUE))

Output:

Method 2: Using left_join

This performs left join on two dataframes which are available in dplyr() package.

Syntax: 

left_join(df1, df2, by='column_name')

where 

• df1 and df2 are the two dataframes
• column_name specifies on which column they are joined

Example: R program to find a let join

R

# load the library
library("dplyr")

# create first dataframe
data1=data.frame('name'=c('siva','ramu','giri','geetha'),
                 'age'=c(21,23,21,20))

# display
print(data1)

# create second dataframe
data2=data.frame('name'=c('siva','ramya','giri','geetha','pallavi'),
                 'marks'=c(21,23,21,20,30))

# display
print(data2)

print("=========================")

# left join on name column
print(left_join(data1, data2, by='name'))

Output: