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Extract column from list in R

  • Last Updated : 26 Mar, 2021

In this article, we are going to create a list of elements and access those columns in R. We are first creating a list with matrix and vectors and access those columns using R.

Approach

  • Create a list

Syntax:

list_name=list(var1, var2, varn..)

  • Assign names to list elements as columns names. We can give names using names() function

Syntax:



names(list_name)=c(var1, var2, varn)

  • Access those columns and elements.

Simple list

Method 1: Using indices

In this method, we simply have to pass the index of the column with the name of the list to extract that specific column.

Example:

R




# Create a list that can hold a vector, and a matrix
list1 <- list(c("sravan", "sudheer", "vani", "radha"), 
              matrix(c(98, 87, 78, 87)))
  
# assign names to the elements in the list.
names(list1) <- c("names", "percentage")
  
# access the column 1
print(list1[1])
  
# access the column 2
print(list1[2])

Output:

Method2: Using $ operator.



In this method, the name of the column to be retrieved has to be passed with its name and name of the list separated by the dollar sign($).

Syntax:

list_name$column_name

Example:

R




# Create a list that can hold a vector, and a matrix
list1 <- list(c("sravan", "sudheer", "vani", "radha"), 
              matrix(c(98, 87, 78, 87)))
  
# assign names to the elements in the list.
names(list1) <- c("names", "percentage")
  
# access the column 1
print(list1$names)
  
# access the column 2
print(list1$percentage)

Output:

A list with different structures

A list can contain a matrix, vector, and a list as arguments to a list but to access them the method remains the same and it has been discussed in the code below.

Example: 

R






# Create a list that can hold a vector, and a matrix and a list
list1 <- list(c("sravan", "sudheer", "vani", "radha"), 
              matrix(c(98, 87, 78, 87)),
              list('vignan', 'vit', 'vvit', 'rvrjc'))
  
# assign names to the elements in the list.
names(list1) <- c("names", "percentage", "college")
  
print("Method 1")
  
# access the column 1
print(list1[1])
  
# access the column 2
print(list1[2])
  
# access the column 3
print(list1[3])
  
print("Method 2")
  
# access the column 1
print(list1$names)
  
# access the column 2
print(list1$percentage)
  
# access the column 3
print(list1$college)

Output:

It is possible to access nested elements using [[]] operator.

Syntax:

list_name[[value]][[value]]…

Example:

R




# Create a list that can hold a vector, and a 
# matrix and a list
list1 <- list(c("sravan", "sudheer", "vani", "radha"), 
              matrix(c(98, 87, 78, 87)),
              list('vignan', 'vit', 'vvit', 'rvrjc'))
  
# access 2nd column first element
print(list1[[2]][[1]])
  
# access 2nd column 
print(list1[[2]])
  
# access 3rd column third element
print(list1[[3]][[3]])

Output:




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