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Count the number of duplicates in R
• Last Updated : 07 Apr, 2021

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.

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