How to Count Duplicates in R (With Examples)

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You can use the following methods to count duplicates in a data frame in R:

Method 1: Count Duplicate Values in One Column

sum(duplicated(df$my_column))

Method 2: Count Duplicate Rows

nrow(df[duplicated(df), ])

Method 3: Count Duplicates for Each Unique Row

library(dplyr)

df %>% group_by_all() %>% count

The following examples show how to use each method in practice with the following data frame in R:

#create data frame
df = data.frame(team=c('A', 'A', 'A', 'A', 'B', 'B', 'B', 'B'),
                position=c('G', 'G', 'G', 'F', 'G', 'G', 'F', 'F'),
                points=c(5, 5, 8, 10, 5, 7, 10, 10))

#view data frame
df

  team position points
1    A        G      5
2    A        G      5
3    A        G      8
4    A        F     10
5    B        G      5
6    B        G      7
7    B        F     10
8    B        F     10

Example 1: Count Duplicate Values in One Column

The following code shows how to count the number of duplicate values in the points column:

#count number of duplicate values in points column
sum(duplicated(df$points))

[1] 4

We can see that there are 4 duplicate values in the points column.

Example 2: Count Duplicate Rows

The following code shows how to count the number of duplicate rows in the data frame:

#count number of duplicate rows
nrow(df[duplicated(df), ])

[1] 2

We can see that there are 2 duplicate rows in the data frame.

We can use the following syntax to view these 2 duplicate rows:

#display duplicated rows
df[duplicated(df), ]

  team position points
2    A        G      5
8    B        F     10

Example 3: Count Duplicates for Each Unique Row

The following code shows how to count the number of duplicates for each unique row in the data frame:

library(dplyr)

#count number of duplicate rows in data frame
df %>% group_by_all() %>% count

# A tibble: 6 x 4
# Groups:   team, position, points [6]
  team  position points     n
         
1 A     F            10     1
2 A     G             5     2
3 A     G             8     1
4 B     F            10     2
5 B     G             5     1
6 B     G             7     1

The n column displays the number of duplicates for each unique row.

Additional Resources

The following tutorials explain how to perform other common tasks in R:

How to Find Duplicate Elements Using dplyr
How to Remove Duplicate Rows in R
How to Remove Duplicate Rows in R so None are Left