Method HasDuplicates

HasDuplicates<T>(IEnumerable<T>)

Checks if sequence contains duplicates.

Declaration

public static bool HasDuplicates<T>(this IEnumerable<T> source)

Parameters

Type	Name	Description
IEnumerable<T>	source	The sequence to check.

Returns

Type	Description
bool	true if any element of the sequence source is duplicated, false otherwise.

Type Parameters

Name	Description
T	The type of the elements in the source sequence.

Remarks

This method executes immediately.

Examples

The following code example demonstrates how to check if a sequence has duplicate values using HasDuplicates.

var seq1 = new[] { "foo", "bar", "baz" };
var seq2 = new[] { "foo", "bar", "baz", "foo", };
var seq3 = new[] { "foo", "bar", "baz", "FOO", };

// determine if a sequence has duplicate items
var result = seq1
    .HasDuplicates();
Console.WriteLine($"Has Duplicates: {result}");

result = seq2
    .HasDuplicates();
Console.WriteLine($"Has Duplicates: {result}");

result = seq3
    .HasDuplicates();
Console.WriteLine($"Has Duplicates: {result}");

// This code produces the following output:
// Has Duplicates: False
// Has Duplicates: True
// Has Duplicates: False

Exceptions

Type	Condition
ArgumentNullException	source is null.

HasDuplicates<T>(IEnumerable<T>, IEqualityComparer<T>?)

Checks if sequence contains duplicates, using the specified element equality comparer.

Declaration

public static bool HasDuplicates<T>(this IEnumerable<T> source, IEqualityComparer<T>? comparer)

Parameters

Type	Name	Description
IEnumerable<T>	source	The sequence to check.
IEqualityComparer<T>	comparer	The equality comparer to use to determine whether or not keys are equal. If null, the default equality comparer for T is used.

Returns

Type	Description
bool	true if any element of the sequence source is duplicated, false otherwise.

Type Parameters

Name	Description
T	The type of the elements in the source sequence.

Remarks

This method executes immediately.

Examples

The following code example demonstrates how to check if a sequence has duplicate values using HasDuplicates.

var seq1 = new[] { "foo", "bar", "baz" };
var seq2 = new[] { "foo", "bar", "baz", "foo", };
var seq3 = new[] { "foo", "bar", "baz", "FOO", };

// determine if a sequence has duplicate items
var result = seq1
    .HasDuplicates(
        StringComparer.OrdinalIgnoreCase);
Console.WriteLine($"Has Duplicates: {result}");

result = seq2
    .HasDuplicates(
        StringComparer.OrdinalIgnoreCase);
Console.WriteLine($"Has Duplicates: {result}");

result = seq3
    .HasDuplicates(
        StringComparer.OrdinalIgnoreCase);
Console.WriteLine($"Has Duplicates: {result}");

// This code produces the following output:
// Has Duplicates: False
// Has Duplicates: True
// Has Duplicates: True

Exceptions

Type	Condition
ArgumentNullException	source is null.

HasDuplicates<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>)

Checks if sequence contains duplicates according to a specified key selector function.

Declaration

public static bool HasDuplicates<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The sequence to check.
Func<TSource, TKey>	keySelector	A function to extract the key for each element.

Returns

Type	Description
bool	true if any element of the sequence source is duplicated, false otherwise.

Type Parameters

Name	Description
TSource	Type of the source sequence.
TKey	The type of key to distinguish elements by.

Remarks

This method executes immediately.

Examples

The following code example demonstrates how to check if a sequence has duplicate values using HasDuplicates.

var seq1 = new[] { "f", "ba", "qax" };
var seq2 = new[] { "f", "ba", "qax", "fuba", };
var seq3 = new[] { "f", "ba", "qax", "FUBA", };

// determine if a sequence has duplicate items
var result = seq1
    .HasDuplicates(
        x => x[0..1]);
Console.WriteLine($"Has Duplicates: {result}");

result = seq2
    .HasDuplicates(
        x => x[0..1]);
Console.WriteLine($"Has Duplicates: {result}");

result = seq3
    .HasDuplicates(
        x => x[0..1]);
Console.WriteLine($"Has Duplicates: {result}");

// This code produces the following output:
// Has Duplicates: False
// Has Duplicates: True
// Has Duplicates: False

Exceptions

Type	Condition
ArgumentNullException	source or keySelector is null.

HasDuplicates<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>, IEqualityComparer<TKey>?)

Checks if sequence contains duplicates according to a specified key selector function, using the specified element equality comparer.

Declaration

public static bool HasDuplicates<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? comparer)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The sequence to check.
Func<TSource, TKey>	keySelector	A function to extract the key for each element.
IEqualityComparer<TKey>	comparer	The equality comparer to use to determine whether or not keys are equal. If null, the default equality comparer for TKey is used.

Returns

Type	Description
bool	true if any element of the sequence source is duplicated, false otherwise.

Type Parameters

Name	Description
TSource	Type of the source sequence.
TKey	The type of key to distinguish elements by.

Remarks

This method executes immediately.

Examples

The following code example demonstrates how to check if a sequence has duplicate values using HasDuplicates.

var seq1 = new[] { "f", "ba", "qax" };
var seq2 = new[] { "f", "ba", "qax", "fuba", };
var seq3 = new[] { "f", "ba", "qax", "FUBA", };

// determine if a sequence has duplicate items
var result = seq1
    .HasDuplicates(
        x => x[0..1],
        StringComparer.OrdinalIgnoreCase);
Console.WriteLine($"Has Duplicates: {result}");

result = seq2
    .HasDuplicates(
        x => x[0..1],
        StringComparer.OrdinalIgnoreCase);
Console.WriteLine($"Has Duplicates: {result}");

result = seq3
    .HasDuplicates(
        x => x[0..1],
        StringComparer.OrdinalIgnoreCase);
Console.WriteLine($"Has Duplicates: {result}");

// This code produces the following output:
// Has Duplicates: False
// Has Duplicates: True
// Has Duplicates: True

Exceptions

Type	Condition
ArgumentNullException	source or keySelector is null.