C# Sort and OrderBy comparison

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I can sort a list using Sort or OrderBy. Which one is faster? Are both working on same algorithm?

List<Person> persons = new List<Person>();
persons.Add(new Person("P005", "Janson"));
persons.Add(new Person("P002", "Aravind"));
persons.Add(new Person("P007", "Kazhal"));

1.

persons.Sort((p1,p2)=>string.Compare(p1.Name,p2.Name,true));

2.

var query = persons.OrderBy(n => n.Name, new NameComparer());

class NameComparer : IComparer<string>
{
    public int Compare(string x,string y)
    {
      return  string.Compare(x, y, true);
    }
}
sql-order-by sorting performance .net c#
6 Answers

In a nutshell :

List/Array Sort() :

  • Unstable sort.
  • Done in-place.
  • Use Introsort/Quicksort.
  • Custom comparison is done by providing a comparer. If comparison is expensive, it might be slower than OrderBy() (which allow to use keys, see below).

OrderBy/ThenBy() :

  • Stable sort.
  • Not in-place.
  • Use Quicksort. Quicksort is not a stable sort. Here is the trick : when sorting, if two elements have equal key, it compares their initial order (which has been stored before sorting).
  • Allows to use keys (using lambdas) to sort elements on their values (eg : x => x.Id). All keys are extracted first before sorting. This might result in better performance than using Sort() and a custom comparer.

Sources: MDSN, reference source and dotnet/coreclr repository (GitHub).

Some of the statements listed above are based on current .NET framework implementation (4.7.2). It might change in the future.

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