Count the number of duplicates in R

In this article, we will see how to find out the number of duplicates in R Programming language. 

It can be done with two methods:

• Using duplicated() function.
• Using algorithm.

Method 1: Using duplicated()

Here we will use duplicated() function of R and dplyr functions.

Approach:

• Insert the “library(tidyverse)” package to the program.
• Create a data frame or a vector.
• Use the duplicated() function and check for the duplicate data.

Syntax: duplicated(x)

Parameters: x: Data frame or a vector

Example 1: Finding duplicate in vector.

Let’s first create a vector and find the position of the duplicate elements in x.

R

x <- c(1, 1, 4, 5, 4, 6)

duplicated(x)

Extract the duplicate elements in x.

R

x <- c(1, 1, 4, 5, 4, 6)

duplicated(x)
x[duplicated(x)]

Here we can see all the elements which are duplicated.

Example 2: Finding duplicate in Dataframe.

Let’s now create a data frame.

R

data <- data.frame(
  emp_id = c (1,1,2,4,5,6,6),
  emp_name = c("Rick","Dan","Michelle",
               "Ryan","Gary","x" , "y"))

display(data)

Here we have a data frame and some items are duplicated, so we have to find the duplicated elements in this data frame.

We will check which column has the duplicated data.

R

duplicated(data$emp_id)

So now find out in emp_id column how many duplicated elements are there.

R

data <- data.frame(
  emp_id = c (1, 1, 2, 4, 5, 6, 6),
  emp_name = c("Rick", "Dan", "Michelle",
               "Ryan", "Gary", "x" , "y"))

duplicated[(data$emp_id), ]

We can see all the duplicated elements in column emp_id.

Method 2: Using algorithm.

Lets us assume we have a data frame with duplicate data, and we have to find out the number of duplicates in that data frame.

R

data <- data.frame(
  emp_id = c (1,1,2,4,5,6,6),
  emp_name = c("Rick","Dan","Michelle","Ryan","Gary","x" , "y"))

sum(table(data$emp_id)-1)

Output:

We can see clearly we have calculated the number of duplicates in the data frame.