Method InnerMergeJoin

InnerMergeJoin<TLeft, TRight, TKey>(IEnumerable<TLeft>, IEnumerable<TRight>, Func<TLeft, TKey>, Func<TRight, TKey>, IComparer<TKey>?)

Performs an inner join on two heterogeneous sequences.

Declaration

public static IEnumerable<(TLeft Left, TRight Right)> InnerMergeJoin<TLeft, TRight, TKey>(this IEnumerable<TLeft> left, IEnumerable<TRight> right, Func<TLeft, TKey> leftKeySelector, Func<TRight, TKey> rightKeySelector, IComparer<TKey>? comparer = null)

Parameters

Type	Name	Description
IEnumerable<TLeft>	left	The first sequence.
IEnumerable<TRight>	right	The second sequence.
Func<TLeft, TKey>	leftKeySelector	A function to extract the join key from each element of the first sequence.
Func<TRight, TKey>	rightKeySelector	A function to extract the join key from each element of the second sequence.
IComparer<TKey>	comparer	An IEqualityComparer<T> to hash and compare keys.

Returns

Type	Description
IEnumerable<(TLeft Left, TRight Right)>	A sequence containing values from an inner join of the two input sequences.

Type Parameters

Name	Description
TLeft	The type of elements in the first sequence.
TRight	The type of elements in the second sequence.
TKey	The type of the key returned by the key selector functions.

Remarks

The result of this method is an `inner`-join. Values are only returned if matching elements are found in both left and right sequences.

This method is implemented using a `merge`-join. The sequences left and right are assumed to be already sorted. Results from using unsorted sequences with this method are undefined. Each sequence is enumerated exactly once in a parallel fashion, until both sequences are fully enumerated.

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to execute an inner merge join of two sequences using InnerMergeJoin.

var people = new Person[]
{
    new("John Doe", 1),
    new("Jane Doe", 6),
    new("Lucy Ricardo", 4),
    new("Ricky Ricardo", 2),
    new("Fred Mertz", 3),
    new("Ethel Mertz", 5),
};

var pets = new Pet[]
{
    new("Bear", 8),
    new("Polly", 2),
    new("Minnie", 2),
    new("Mittens", 1),
    new("Patches", 1),
    new("Paws", 1),
};

var results = people.OrderBy(p => p.PersonId)
    .InnerMergeJoin(
        pets.OrderBy(p => p.PersonId),
        p => p.PersonId,
        p => p.PersonId);

foreach (var (person, pet) in results)
{
    Console.WriteLine($"({person.Name}, {pet?.Name})");
}

// This code produces the following output:
// (John Doe, Mittens)
// (John Doe, Patches)
// (John Doe, Paws)
// (Ricky Ricardo, Polly)
// (Ricky Ricardo, Minnie)

record Person(string Name, int PersonId);
record Pet(string Name, int PersonId);

Exceptions

Type	Condition
ArgumentNullException	left, right, leftKeySelector, or rightKeySelector is null.

InnerMergeJoin<TLeft, TRight, TKey, TResult>(IEnumerable<TLeft>, IEnumerable<TRight>, Func<TLeft, TKey>, Func<TRight, TKey>, Func<TLeft, TRight, TResult>, IComparer<TKey>?)

Performs an inner join on two heterogeneous sequences.

Declaration

public static IEnumerable<TResult> InnerMergeJoin<TLeft, TRight, TKey, TResult>(this IEnumerable<TLeft> left, IEnumerable<TRight> right, Func<TLeft, TKey> leftKeySelector, Func<TRight, TKey> rightKeySelector, Func<TLeft, TRight, TResult> bothResultSelector, IComparer<TKey>? comparer = null)

Parameters

Type	Name	Description
IEnumerable<TLeft>	left	The first sequence.
IEnumerable<TRight>	right	The second sequence.
Func<TLeft, TKey>	leftKeySelector	A function to extract the join key from each element of the first sequence.
Func<TRight, TKey>	rightKeySelector	A function to extract the join key from each element of the second sequence.
Func<TLeft, TRight, TResult>	bothResultSelector	A function to create a result element from two matching elements.
IComparer<TKey>	comparer	An IEqualityComparer<T> to hash and compare keys.

Returns

Type	Description
IEnumerable<TResult>	A sequence containing results projected from an inner join of the two input sequences.

Type Parameters

Name	Description
TLeft	The type of elements in the first sequence.
TRight	The type of elements in the second sequence.
TKey	The type of the key returned by the key selector functions.
TResult	The type of the result elements.

Remarks

The result of this method is an `inner`-join. Values are projected using bothResultSelector only if matching elements are found in both left and right sequences.

This method is implemented using a `merge`-join. The sequences left and right are assumed to be already sorted. Results from using unsorted sequences with this method are undefined. Each sequence is enumerated exactly once in a parallel fashion, until both sequences are fully enumerated.

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to execute an inner merge join of two sequences using InnerMergeJoin.

var people = new Person[]
{
    new("John Doe", 1),
    new("Jane Doe", 6),
    new("Lucy Ricardo", 4),
    new("Ricky Ricardo", 2),
    new("Fred Mertz", 3),
    new("Ethel Mertz", 5),
};

var pets = new Pet[]
{
    new("Bear", 8),
    new("Polly", 2),
    new("Minnie", 2),
    new("Mittens", 1),
    new("Patches", 1),
    new("Paws", 1),
};

var results = people.OrderBy(p => p.PersonId)
    .InnerMergeJoin(
        pets.OrderBy(p => p.PersonId),
        p => p.PersonId,
        p => p.PersonId,
        (person, pet) => $"({person.Name}, {pet.Name})");

foreach (var str in results)
    Console.WriteLine(str);

// This code produces the following output:
// (John Doe, Mittens)
// (John Doe, Patches)
// (John Doe, Paws)
// (Ricky Ricardo, Polly)
// (Ricky Ricardo, Minnie)

record Person(string Name, int PersonId);
record Pet(string Name, int PersonId);

Exceptions

Type	Condition
ArgumentNullException	left, right, leftKeySelector, rightKeySelector, or bothResultSelector is null.