Data Structure: List

↪ Creating a list

A list is used for storing an ordered set of elements. While a vector requires all its elements to be of the same type, a list allows different types of elements.

The list() function is used for creating a list.

      x = list("Chimpanjee",10, 175.2)
      x

      ---Output---
      [[1]]
      [1] "Chimpanjee"
 
      [[2]]
      [1] 10
 
      [[3]]
      [1] 175.2

Creating a list with a tag.

      x = list(name="Chimpanjee", age=10, height=175.2)
      x

      ---Output---
      $name
      [1] "Chimpanjee"
 
      $age
      [1] 10
 
      $height
      [1] 175.2

Creating a list using as.list() function.

      students = c("Mark","Philip","Mary")
      x <- as.list(students)
      x

      ---Output---
      [[1]]
      [1] "Mark"
 
      [[2]]
      [1] "Philip"
 
      [[3]]
      [1] "Mary"

Creating a list using vectors.

      students = c("Mark","Philip","Mary")
      grade = c(6,7,6)
 
      class = list(students,grade)
      class

      ---Output---
      [[1]]
      [1] "Mark"   "Philip" "Mary"  
 
      [[2]]
      [1] 6 7 6

Data Structure: List

↪ Accessing the list of elements

Take the previous example of a list class.

      students = c("Mark","Philip","Mary")
      grade = c(6,7,6)
      class = list(students,grade)

      class[[1]]         # Prints [1] "Mark"   "Philip" "Mary" 
      class[2]           # [[1]]
                         #  [1] 6 7 6

Elements of a particular vector can be specified by using the required position enclosed in [[i]][j] format.

      class[[1]][2]      # Prints [1] "Philip"

When the list is created with tags, the elements can be accessed using the tag name.

      x = list(name="Chimpanjee",
               age=10, height=175.2)
      x$name                           # Prints [1] "Chimpanjee"