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R – Get Element by Index in a Vector

Vectors are a common data structure in R. We generally use vectors to store a sequence of values of the same type. In this tutorial, we will look at how to get an element by its index in a vector in R with the help of some examples.

How to get an element by index in a vector?

Elements in a vector are indexed starting from 1. Use the [] notation to get a vector element by its index in R. The following is the syntax –

# get element at index i in a vector
vec[i]

It returns the element present in the vector at the ith index.

Examples

Let’s look at some examples of extracting elements using their respective index in R. First, we will create a vector that we will be using throughout this tutorial.

# create a vector
vec <- c(10, 20, 30, 40, 50)
# display the vector
print(vec)

Output:

[1] 10 20 30 40 50

Get the value at an index in a vector

Let’s use the above syntax to get the value at the index 2 in the vec vector.

# get element in vector at index 2
print(vec[2])

Output:

[1] 20

We get 20 as the output, which is the value at the second index in the vector, vec. Let’s now look at some more specific use-cases.

Get the first element in a vector

Let’s get the first value in the above vector. We know that a vector is indexed starting from 1 in R. So, the first value is present at index 1. Let’s use the above syntax to get the first value.

# get the first element in the vector
print(vec[1])

Output:

[1] 10

We get the first value in the above vector as 10.

Get the last element in a vector

You can similarly get the last value in a vector. The last value will present at the index which is equal to the length of the vector. You can use the length() function in R to get the length of a vector.

# get the last element in the vector
print(vec[length(vec)])

Output:

[1] 50

Here, we first use the length() function to find the length of the vector (which is the same as the index of the last element) and then use the [] notation to get the value at that index. We get 50 as the last element in the above vector.

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Author

  • Piyush

    Piyush is a data scientist passionate about using data to understand things better and make informed decisions. In the past, he's worked as a Data Scientist for ZS and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.