How to Set Data Frame Column as Index in R (With Example)


Data frames in R do not have an “index” column like data frames in pandas might.

However, data frames in R do have row names, which act similar to an index column.

You can use one of the following methods to set an existing data frame column as the row names for a data frame in R:

Method 1: Set Row Names Using Base R

#set specific column as row names
rownames(df) <- df$my_column

#remove original column from data frame
df$my_column <- NULL

Method 2: Set Row Names Using Tidyverse Package

library(tidyverse)

#set specific column as row names
df <- df %>% column_to_rownames(., var = 'my_column')

Method 3: Set Row Names When Importing Data

#import CSV file and specify column to use as row names
df <- read.csv('my_data.csv', row.names='my_column')

The following examples show how to use each method in practice.

Example 1: Set Row Names Using Base R

Suppose we have the following data frame in R:

#create data frame
df <- data.frame(ID=c(101, 102, 103, 104, 105),
                 points=c(99, 90, 86, 88, 95),
                 assists=c(33, 28, 31, 39, 34),
                 rebounds=c(30, 28, 24, 24, 28))

#view data frame
df

   ID points assists rebounds
1 101     99      33       30
2 102     90      28       28
3 103     86      31       24
4 104     88      39       24
5 105     95      34       28

We can use the following code to set the ID column as the row names:

#set ID column as row names
rownames(df) <- df$ID

#remove original ID column from data frame
df$ID <- NULL

#view updated data frame
df

    points assists rebounds
101     99      33       30
102     90      28       28
103     86      31       24
104     88      39       24
105     95      34       28

The values from the ID column are now the row names for the data frame.

Example 2: Set Row Names Using Tidyverse Package

The following code shows how to use the column_to_rownames() function from the tidyverse package to set the row names equal to the ID column in the data frame:

library(tidyverse)

#create data frame
df <- data.frame(ID=c(101, 102, 103, 104, 105),
                 points=c(99, 90, 86, 88, 95),
                 assists=c(33, 28, 31, 39, 34),
                 rebounds=c(30, 28, 24, 24, 28))

#set ID column as row names
df <- df %>% column_to_rownames(., var = 'ID')

#view updated data frame
df

    points assists rebounds
101     99      33       30
102     90      28       28
103     86      31       24
104     88      39       24
105     95      34       28

Notice that this result matches the one from the previous example.

Example 3: Set Row Names When Importing Data

Suppose we have the following CSV file called my_data.csv:

We can use the following code to import the CSV file and set the row names to be equal to the ID column when importing:

#import CSV file and specify ID column to use as row names
df <- read.csv('my_data.csv', row.names='ID')

#view data frame
df

    points assists rebounds
101     99      33       30
102     90      28       28
103     86      31       24
104     88      39       24
105     95      34       28

Notice that the values from the ID column are used as the row names in the data frame.

Additional Resources

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

How to Remove Rows from Data Frame in R Based on Condition
How to Replace Values in Data Frame in R
How to Drop Columns from Data Frame in R

Leave a Reply

Your email address will not be published.