Find Index of First Occurrence of Item in Array in Swift

An array is used to store elements of the same data type in order.

Here we will learn how to write a swift program to find the index of the first occurrence of the specified item in the array.

To achieve that we are going to use the following methods to find the index of the first occurrence of the array element ?

• Using user-defined function

• Using firstIndex() function

Method 1: Using user-defined function

To find the index of the first occurrence of the specified element in the array we create a function which iterate through each elements and their indexes and check if the current value is equal to the specified element. If yes, then it return that current index. If the loop ends and the element does not fount, then it return nil.

Algorithm

• Step 1 ? Create a function.

• Step 2 ? Run a for loop.

• Step 3 ? Check if the current element is equal to specified element. If yes then return the current index.

• Step 4 ? Return nil if the loop ends and the specified element not found.

• Step 5 ? Create an array and pass it to the function along with the element.

• Step 6 ? Print the result

Example

Following Swift program to find the index of the first occurrence of the specified item in the array.

import Foundation
import Glibc

// Function to find the index of the first occurrence of the specified item in the array
func findFirstIndex(ele: Int, in arr: [Int]) -> Int? {
   for (index, value) in arr.enumerated() {
      if value == ele {
         return index
      }
   }
   return nil
}

// Creating an array of integer type
let numbers = [12, 9, 3, 6, 88, 23, 4, 6, 4, 23, 6]
if let index = findFirstIndex(ele: 6, in: numbers) {
   print("The first occurrence of 6 is at index \(index)")
} else {
   print("Element 6 is not found in the give array")
}

Output

The first occurrence of 6 is at index 3

Here in the above code, we have an array of integer type. Now we create a function named findFirstIndex() and pass the element and the array in it. In this function, we run a for loop which iterates through each element of the original, and using enumerated() function we get the index and the element. Inside the for loop, we check if the current element is equal to the specified element. If the current element is equal to the specified element, then this function return the current index. If the loop ends and no element is equal to the specified element, then this function returns nil.

Method 2: Using firstIndex(of:) function

Swift provides an inbuilt function named as firstIndex(of:) function. This function returns the first index where the specified elements appear in the given array. If the specified element is not found in the given array, then it will return nil.

Syntax

Func firstIndex(of: Element)

Here, Element represent the item to search for in the array.

Algorithm

• Step 1 ? Create an array of integer type.

• Step 2 ? Use if-else to check the index of the first occurrence of the specified element in the array using firstIndex(of:) function.

• Step 3 ? If the element found in the given array, then display the index value.

• Step 4 ? If the element does not found, then print "Element is not found".

Example

Following Swift program to find the index of the first occurrence of the specified item in the array.

import Foundation
import Glibc

// Creating an array of integer type
let mArray = [20, 3, 3, 4, 21, 4, 7, 10, 8, 4, 2]

// Finding the index of the first occurrence of the specified item in the array
if let index = mArray.firstIndex(of: 4) {
   print("The first occurrence of 4 is at index \(index)")
} 
else {
   print("Element 4 is not found in the given array")
}

Output

The first occurrence of 4 is at index 3

Here in the above code, we have an array of integer. Then we uses firstIndex(of:) function to find the index of the first occurrence of the element 4 in the array. If the number is found in the array, then display the element along with its index value. Otherwise display element not found. Here we use if let with the firstIndex(of:) function because this function return optional Int value so unwrap to using if let.

Conclusion

In this article we have used two different methods to find the index of the first occurrence of the specified item in the array. In the first method, we have used a user-defined function, whereas in the second example, we have used ian nternal function - firstIndex(of:) to find the index.