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In R, you can set a data frame column as an index by using the set_index() function. This function requires a parameter of the column name you want to set as the index. For example, if you have a data frame called df, and you want to set the column “Name” as the index, you would use the code df = df.set_index(“Name”). This will set “Name” as the index of the data frame. You can also use the set_index() function to set multiple columns as the index.
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
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.
The following tutorials explain how to perform other common tasks in R: