Return the total elements in a sequence as a 64-bit signed integer in C#

The LongCount() method in C# returns the total number of elements in a sequence as a 64-bit signed integer (long). This method is particularly useful when dealing with large datasets where the element count might exceed the range of a regular 32-bit integer.

The LongCount() method is available in both LINQ to Objects and LINQ to Entities, and can be used with any IEnumerable<T> or IQueryable<T> collection.

Syntax

Following is the syntax for using LongCount() method −

public static long LongCount<TSource>(this IEnumerable<TSource> source)
public static long LongCount<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)

Parameters

• source − The sequence to count elements in.

• predicate − (Optional) A function to test each element for a condition.

Return Value

Returns a long value representing the total number of elements in the sequence, or the number of elements that satisfy the condition if a predicate is provided.

Using LongCount() on Arrays

Here's how to count all elements in an array −

using System;
using System.Linq;

class Demo {
   static void Main() {
      string[] num = { "One", "Two", "Three", "Four", "Five" };
      long res = num.LongCount();
      Console.WriteLine("{0} elements", res);
   }
}

The output of the above code is −

5 elements

Using LongCount() with Predicate

You can also count elements that meet a specific condition −

using System;
using System.Linq;

class Demo {
   static void Main() {
      int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
      long evenCount = numbers.LongCount(x => x % 2 == 0);
      long greaterThanFive = numbers.LongCount(x => x > 5);
      
      Console.WriteLine("Even numbers: {0}", evenCount);
      Console.WriteLine("Numbers greater than 5: {0}", greaterThanFive);
   }
}

The output of the above code is −

Even numbers: 5
Numbers greater than 5: 5

LongCount() vs Count()

Using LongCount() with Collections

using System;
using System.Collections.Generic;
using System.Linq;

class Demo {
   static void Main() {
      List<string> fruits = new List<string> { "Apple", "Banana", "Orange", "Grapes", "Mango" };
      long totalFruits = fruits.LongCount();
      long fruitsStartingWithA = fruits.LongCount(f => f.StartsWith("A"));
      
      Console.WriteLine("Total fruits: {0}", totalFruits);
      Console.WriteLine("Fruits starting with 'A': {0}", fruitsStartingWithA);
   }
}

The output of the above code is −

Total fruits: 5
Fruits starting with 'A': 1

Conclusion

The LongCount() method is essential when working with large datasets where element counts might exceed the 32-bit integer limit. It provides the same functionality as Count() but returns a 64-bit long integer, making it suitable for big data scenarios and ensuring your applications can handle massive collections without overflow exceptions.