Max (LINQ)

Enumerable.Max is extension method from System.Linq namespace. It returns maximal value of numeric collection.

Max for Numeric Types

Gets maximal number from list of integer numbers.

var numbers = new List<int> { 1, 8, 3, 2 }; int maxNumber = numbers.Max(); // maxNumber: 8

Gets maximal number from list of decimal numbers.

var numbers = new List<decimal> { 1.0m, 8.1m, 3.3m, 2.0m }; decimal maxNumber = numbers.Max(); // maxNumber: 8.1

Calling Max on empty collection throws exception.

var numbers = new List<int>(); // empty list int maxNumber = numbers.Max(); // throws InvalidOperationException

Max for Nullable Numeric Types

Gets maximal number from list of nullable integers.

var numbers = new List<int?> { 1, 8, null, 3 }; int? maxNumber = numbers.Max(); // maxNumber: 8

Returns null if the collection contains only null values.

var numbers = new List<int?> { null }; int? maxNumber = numbers.Max(); // maxNumber: null

Returns null if the collection is empty.

var numbers = new List<int?>(); // empty list int? maxNumber = numbers.Max(); // maxNumber: null

Max with Selector

This example gets length of the longest string.

var stringList = new List<string> { "1", "88888888", "333", "22" }; // these two lines do the same int maxLength = stringList.Select(x => x.Length).Max(); // maxLength: 8 int maxLength = stringList.Max(x => x.Length); // maxLength: 8

Max for Types Implementing IComparable

LINQ method Max can be used also on collection of custom type (not numeric type like int or decimal). The custom type have to implement IComparable interface.

Lets have custom type Money which implements IComparable.

public struct Money : IComparable<Money> { public Money(decimal value) : this() { Value = value; } public decimal Value { get; private set; } public int CompareTo(Money other) { return Value.CompareTo(other.Value); } }

And this is usage of Max method on the Money collection.

var amounts = new List<Money> { new Money(30), new Money(10) }; Money maxAmount = amounts.Max(); // maxAmount: Money with value 30

Max with Query Syntax

LINQ query expression to get maximal item in the collection.

var list = new List<int> { 1, 8, 3, 2 }; int maxNumber = (from x in list select x).Max(); // maxNumber: 8

LINQ query expression to get maximal item which matches specified predicate.

var list = new List<int> { 1, 8, 3, 2 }; int maxNumber = (from x in list where x < 5 select x).Max(); // maxNumber: 3

LINQ query expression to get maximal string length using selector.

var list = new List<string> { "1", "88888888", "333", "22" }; int maxLength = (from x in list select x.Length).Max(); // maxLength: 8

Max with Group By

This example shows how to get maximal value per group. Lets have players. Each player belongs to a team and have a score. Team best score is maximal score of players in a team.

var players = new List<Player> { new Player { Name = "Alex", Team = "A", Score = 10 }, new Player { Name = "Anna", Team = "A", Score = 20 }, new Player { Name = "Luke", Team = "L", Score = 60 }, new Player { Name = "Lucy", Team = "L", Score = 40 }, }; var teamBestScores = from player in players group player by player.Team into playerGroup select new { Team = playerGroup.Key, BestScore = playerGroup.Max(x => x.Score), }; // teamBestScores is collection of anonymous objects: // { Team = "A", BestScore = 20 } // { Team = "L", BestScore = 60 }

Max Implementation

This is .NET Framework implementation of Enumerable.Max method for collection of numeric type (in this case IEnumerable<int>). Note that it throws the exception for an empty collection on the last line (throw Error.NoElements();)).

public static int Max(this IEnumerable<int> source) { if (source == null) throw Error.ArgumentNull("source"); int value = 0; bool hasValue = false; foreach (int x in source) { if (hasValue) { if (x > value) value = x; } else { value = x; hasValue = true; } } if (hasValue) return value; throw Error.NoElements(); }

This is .NET Framework implementation of Enumerable.Max method for collection of nullable numeric type (in this case IEnumerable<int?>). Note that it returns null for an empty collection (int? value = null;). Also notice that it returns null if all values in the collection are null.

public static int? Max(this IEnumerable<int?> source) { if (source == null) throw Error.ArgumentNull("source"); int? value = null; foreach (int? x in source) { if (value == null || x > value) value = x; } return value; }

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