Linq performance with Count() and Any()

Recently I was using resharper to refactor some of my code and found that it was suggesting to use any() extension method instead of count() method in List<T>. I was really keen about performance and found that resharper was right. There is huge performance difference between any() and count() if you are using count() just to check whether list is empty or not.

Difference between Count() and Any():

In Count() method code will traverse all the list and get total number of objects in list while in Any() will return after examining first element in the sequence. So in list where we have many object it will be significant execution time if we use count().

Example:

Let’s take an example to illustrate this scenario. Following is a code for that.
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main() {

            //Creating List of customers
            List<Customer> customers = new List<Customer>();
            for (int i = 0; i <= 100; i++) {
                Customer customer = new Customer {
                    CustomerId = i,
                    CustomerName = string.Format("Customer{0}", i)
                };
                customers.Add(customer);
            }

            //Measuring time with count
            Stopwatch stopWatch = new Stopwatch();
            stopWatch.Start();
            if (customers.Count > 0) {
                Console.WriteLine("Customer list is not empty with count");
            }
            stopWatch.Stop();
            Console.WriteLine("Time consumed with count: {0}", stopWatch.Elapsed);

            //Measuring time with any
            stopWatch.Restart();
            if (customers.Any()) {
                Console.WriteLine("Customer list is not empty with any");
            }
            stopWatch.Stop();
            Console.WriteLine("Time consumed with count: {0}", stopWatch.Elapsed);
        }
    }

    public class Customer
    {
        public int CustomerId { get; set; }
        public string CustomerName { get; set; }
    }
}

Here in the above code you can see that I created ‘Customer’ class which has simple two properties ‘CustomerId’ and ‘CustomerName’. Then in Main method I have created a list of customers and used for loop and object intializer to fill customers list. After that I have written a code to measure time for count and any with ‘Stop watch’ class and printing CPU ticks. It’s pretty simple.

Now let’s run this console application to see output.

Performance diffrence between Any() and Count() in c#

Conclusion:

Here in the above example you can see there is huge performance benefit of using any() instead of count() when we are checking whether list<T> is empty or not.

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6 comments:

  1. Have you tried to measure this multiple times or switch the if's? It could be that the second call was faster cause of optimization.
    Otherwise this would be fascinating and a bit weird.

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  2. Your conclusion is (mostly) correct, in that Enumerable.Count() is generally slower than Enumerable.Any(), but your method is flawed.

    First, you are not even using LINQ's Count() extension, but rather List.Count property. And, more importantly, you are including Console.WriteLine calls in your timings, which affects the result.

    If I modify your code to just time 'customers.Count > 0' and 'customers.Any()', the results are completely different (Count = 00:00:00.0000018, Any() = 00:00:00.0001110). This is expected, as accessing List.Count doesn't iterate through the list and is internally maintained by List as elements are added and removed.

    However, due to LINQ being heavily optimised, even if you used Count() it would *still* be faster than using Any() on List. This is because Count() recognises that your collection implements ICollection and so returns the value of its Count property immediately, while Any() always calls GetEnumerator() and tries to advance it.

    ReplyDelete
  3. @google-90118b81f48cfb8666f1e1d44a427168:disqus - Thanks for your inputs and will check it.

    ReplyDelete
  4. @google-90118b81f48cfb8666f1e1d44a427168:disqus - Hi thanks for your input. I will definitely check this

    ReplyDelete
  5. I measured with: no Console.WriteLine(), 10k lists with 50 Customers, 10 iterations, in Release mode.


    In my case:
    - List.Count() is more than 2 times faster then List.Any()

    - List.Count is more than 2 times then List.Count() and more than 5 times faster then List.Any()

    The conclusion should be opposite: Use 'List.Count == 0' instead of List.Any() when checking if List is empty or not.

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