Extract column from list in R

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: