What is which() in R?

Overview

The which() function is used to get the position of the specified argument value in a logical vector. It takes a logical vector as an argument. Otherwise, it throws an error.

Syntax

Parameters

It takes the following argument values.

x: This is the input logical vector.
arr.ind: If x is an array, arr.ind will return indexes of the array. Its default value is FALSE.
useNames: This is the dimension name/s of an array. Its default value is TRUE.

Return value

It returns the indexes of specified values in the logical vector.

Example

Let's use the which() function to elaborate on its different use cases. It helps in filtering and manipulating the data.

Note: The cat() method in R is used to print to the screen or in a file.

# Program to show how to use which() function in program
# Check position of ASCII characters
cat("Using which() to get the position of letters of the English alphabet\n")
which(letters== "e")
which(letters== "d")
which(letters== "u")
which(letters== "c")
which(letters== "a")
which(letters== "t")
which(letters== "i")
which(letters== "v")
which(letters== "e")
# Creating a vector of random values
data <- c(1, 2, 3, 4, 6, 10, 8, 7, 5, 10)
cat("Using which to get index of number 10\n")
which(data == 10)
cat("Get indexes of numbers less than 8\n")
which(data < 8)