Merge Two data.table Objects in R

Last Updated : 23 Aug, 2021

data.table is a package that is used for working with tabular data in R. It provides an enhanced version of “data.frames”, which are the standard data structure for storing data in base R.

Installation

Installing “data.table” package is no different from other R packages. Its recommended to run “install.packages()” to get the latest version on the CRAN repository.

Syntax:

install.packages('data.table')

The syntax of data.table is shown in the image below :

The first parameter of “data.table” i refers to rows. It implies subsetting rows.
The second parameter of “data.table” j refers to columns. It implies subsetting columns (dropping / keeping).
The third parameter of “data.table” by refers to adding a group so that all calculations would be done within a group.

For merging the same syntax is used except it is preceded by merge.

Syntax:

merge.data.table

Example: R program to merge two data.table objects

R

# Load data.table package
library(“data.table”)

print(“first class”)

# Create first data.table
class1 <- data.table(stu_name = c('Naveen','Nupur','Ritika','Praveen'), Subjects = c('Hindi','English','Maths','Science'), Marks1 = c(89,78,72,64)) # Print first data.table print(class1) print("second class") # Create second data.table class2 <- data.table(stu_name = c('Naveen','Nupur','Ritika','Praveen'), Subjects = c('Hindi','English','Maths','Science'), Marks2 = c(56,64,53,88)) # Print second data.table print(class2) print("merge first and second class") # Merge data.tables merge_class <- merge.data.table(class1, class2, by.x = "Subjects", by.y = "Subjects") # Print merged data.table print(merge_class)

Output: