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How to get a range of indices of items in a list in R

Onyejiaku Theophilus Chidalu

Overview

The items of a list can be accessed using their index numbers. In R, the first character of a string, list, or vector has its index value or position as 1. For example, the first character “H” of the string “Hello” has the index value 1, the second character “e” has index value 2, and so on.

Accessing the items of a list

To access the list items as earlier stated, we specify their index value or position in the list.

Example

mylist <- list("orange", "pear", "cashew")

# accessing the first item/index 1 of the list
mylist[1]
Accessing a list

Explanation

We can see from the code above that we can access the first item ("orange") of the list by simply specifying its index value 1.

Getting the range of indices of items

We use the : operator to specify a range of items’ indices of a list, where to start, and where to end.

In the code below, we want to return the list items, starting from the second item to the fourth item.

Example

# creating a list
mylist <- list("mango", "orange", "pear", "apple", "lemon", "cashew")

# specifying from range 2 to 4
(mylist)[2:4]
Specifying the range of indexes of items of a list

Explanation

In the code above, we create a list mylist with 5 items using the list() function. We used the : operator to return a range of list indices from index 2 to index 4.

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Onyejiaku Theophilus Chidalu
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