C# - the fastest way to iterate over dictionary

Having a big dictionary, say 1M of <double,double> samples – what is the fastest way to iterate over it?
Comparing 3 options (iterate over KeyValuePair in the dictionary, iterate over Values collection and iterate over Keys collection) – below is code and timing comparison results.
// Of course if you iterating over Keys collection and accessing the value by key – it would be the slowest case.

// Create sample dictionary

var random = new Random();

var randomDictionaryOfDoubles =

    Enumerable.Repeat(0, 1000000).Select(

        i => Convert.ToDouble(random.Next()))

        .Distinct().OrderBy(i=>i)

        .ToDictionary(i => i);

double total = 0.0;

var stopWatch = new Stopwatch();

//Console.WriteLine("Starting KVP");

stopWatch.Reset();

stopWatch.Start();

foreach (KeyValuePair<double, double> kvp in randomDictionaryOfDoubles)

{

    total += (kvp.Value);

}

stopWatch.Stop();

Console.WriteLine("KVP took:    {0} Total = {1}", stopWatch.Elapsed, total);

//Console.WriteLine("Starting Values");

total = 0.0;

stopWatch.Reset();

stopWatch.Start();

// To get the values alone, use the Values property.

Dictionary<double, double>.ValueCollection valueColl = randomDictionaryOfDoubles.Values;

foreach (double d in valueColl)

{

    total += d;

}

stopWatch.Stop();

Console.WriteLine("Values took: {0} Total = {1}", stopWatch.Elapsed, total);

//Console.WriteLine("Starting keys");

total = 0.0;

stopWatch.Reset();

stopWatch.Start();

// To get the keys alone, use the Keys property.

Dictionary<double, double>.KeyCollection keyColl = randomDictionaryOfDoubles.Keys;

foreach (double d in keyColl)

{

    total += d;

}

stopWatch.Stop();

Console.WriteLine("Keys took:   {0} Total = {1}", stopWatch.Elapsed, total);

Console.ReadLine();

Here are results:

Method	Time spent in iteration
Over key-value pairs	00:00:00.1854684
Over Values collection	00:00:00.1221380
Over Keys collection	00:00:00.0955291

Related article: http://dotnetperls.com/dictionary-lookup

Technorati Теги: C#,Dictionary,performance