C# .NET Programming Blog

Microsoft .net framework 3.5 introduced the Language Integrated Query (Linq) feature. Linq provides a set of query operators to filter, join and perform other such data related operations on various types datasources such as lists, dictionaries, datasets etc.

In this article we perform a simple filter operation on a collection of data stored in a list using the traditional foreach loop method and the linq method and compare the performance statistics.

To test the two methods we prepare a sample list object filled with 10,000,000 random numbers.

Numeric Collection

The first case we consider a list of random integer which has to be filtered to find out how many number generated are greater than 1,000,000. We implement a simple foreach loop filter as shown below.

Show Code

class Program
{
    static void Main(string[] args)
    {
        List<int> sample = GenerateSample();
        int count = 0;
        DateTime start;

        /* Using Foreach Loop */
        start = DateTime.Now;

        foreach (int number in sample)
            if (number > 1000000)
                count++;

        Console.WriteLine("Using Foreach loops: " +
            (DateTime.Now - start).TotalMilliseconds + " ms");

        /* Using Linq Query */
        start = DateTime.Now;

        count = (from number in sample where number > 1000000
                     select number).Count();

        Console.WriteLine("Using Linq Query: " +
            (DateTime.Now - start).TotalMilliseconds + " ms");

        Console.ReadKey();
    }

    static List<int> GenerateSample()
    {
        List<int> sample = new List<int>();
        Random random = new Random();

        for (int i = 0; i < 10000000; i++)
            sample.Add(random.Next());

        return sample;
    }
}

The result for numeric collection:

String Collection

For testing a string collection we take the same random number list in string format and filter out all those strings that start with 10.

Show Code

class Program
{
    static void Main(string[] args)
    {
        List<string> sample = GenerateSample();
        int count = 0;
        DateTime start;

        /* Using Foreach Loop */
        start = DateTime.Now;

        foreach (string number in sample)
            if (number.StartsWith("10"))
                count++;

        Console.WriteLine("Using Foreach Loop: " +
            (DateTime.Now - start).TotalMilliseconds + " ms");

        /* Using Linq Query */
        start = DateTime.Now;

        count = (from number in sample where number.StartsWith("10")
                     select number).Count();

        Console.WriteLine("Using Linq Query: " +
           (DateTime.Now - start).TotalMilliseconds + " ms");

        Console.ReadKey();
    }

    static List<string> GenerateSample()
    {
        List<string> sample = new List<string>();
        Random random = new Random();

        for (int i = 0; i < 10000000; i++)
            sample.Add(random.Next().ToString());

        return sample;
    }
}

The result for string collection:

Conclusion

From the above results its quite clear that for performing operations like filtering on integer or numeric collections the traditional foreach loop filters execute faster.

However for filtering string collections using string operations susch as StrartsWith(), Substring() etc, linq is much faster.

Download Sample
Linq Filter Samples