Method HasDuplicates

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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.
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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.
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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.
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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.