Finding the Last Occurrence of Characters in C# Strings with `LastIndexOfAny()`

Learn how to use C#'s `LastIndexOfAny()` method to efficiently find the last occurrence of any character from a specified array within a string. This tutorial explains `LastIndexOfAny()`'s functionality, its overloads, and provides examples demonstrating its application in string manipulation tasks.

Finding the Last Occurrence of Characters in C# Strings with `LastIndexOfAny()`

Understanding `LastIndexOfAny()`

The C# `LastIndexOfAny()` method finds the index (position) of the last occurrence of any character from a specified array of characters within a string. It searches from the end of the string towards the beginning, returning the index of the last found character or -1 if none of the specified characters are found. The search is case-sensitive by default.

`LastIndexOfAny()` Method Signatures

The `LastIndexOfAny()` method has several overloads:

public int LastIndexOfAny(char[] anyOf);: Searches the entire string.
public int LastIndexOfAny(char[] anyOf, int startIndex);: Searches from a specified starting index towards the beginning of the string.
public int LastIndexOfAny(char[] anyOf, int startIndex, int count);: Searches within a specified range.

Example 1: Finding the Last Occurrence

This example finds the last occurrence of either 'r' or 'b' in the string "abracadabra".

C# Code

using System;

public class LastIndexOfAnyExample {
    public static void Main(string[] args) {
        string str = "abracadabra";
        char[] charsToFind = { 'r', 'b' };
        int index = str.LastIndexOfAny(charsToFind);
        Console.WriteLine(index); // Output: 9 (index of last 'r')
    }
}

    

Example 2: Different Characters

This example demonstrates that the method finds the last occurrence from the provided set of characters. In this example, the last occurrence of either 't' or 'b' is found at index 8.

C# Code

using System;

public class LastIndexOfAnyExample {
    public static void Main(string[] args) {
        string str = "abracadabra";
        char[] charsToFind = { 't', 'b' };
        int index = str.LastIndexOfAny(charsToFind);
        Console.WriteLine(index); // Output: 8 (index of last 'b')
    }
}

    

Conclusion

The `LastIndexOfAny()` method is a very useful tool for finding the last occurrence of any character from a given set within a string. Its ability to search from the end of the string, specify a start index and a range, enhances the efficiency and adaptability of string manipulation operations in C#.