Method StartsWith

StartsWith<T>(IEnumerable<T>, IEnumerable<T>)

Determines whether the beginning of the first sequence is equivalent to the second sequence, using the default equality comparer.

Declaration

public static bool StartsWith<T>(this IEnumerable<T> first, IEnumerable<T> second)

Parameters

Type	Name	Description
IEnumerable<T>	first	The sequence to check.
IEnumerable<T>	second	The sequence to compare to.

Returns

Type	Description
bool	true if first begins with elements equivalent to second.

Type Parameters

Name	Description
T	Type of elements.

Remarks

This is the IEnumerable<T> equivalent of StartsWith(string).

This method executes immediately.

Examples

The following code example demonstrates how to check that one sequence starts with the same elements as another sequence using StartsWith.

var sequence = new[]
{
    "BAR",
    "foo",
    "Baz",
    "Qux",
    "BAZ",
    "FOO",
    "bAr",
    "baz",
    "fOo",
    "BaZ",
};

// check that sequence starts with a known sequence of values
var result = sequence
    .StartsWith(new[] { "BAR", "foo", "Baz", });

Console.WriteLine($"StartsWith ['BAR', 'foo', 'Baz']: {result}");

result = sequence
    .StartsWith(new[] { "bar", "foo", "Baz", });

Console.WriteLine($"StartsWith ['bar', 'foo', 'Baz']: {result}");

result = sequence
    .StartsWith(new[] { "foo", "Baz", });

Console.WriteLine($"StartsWith ['foo', 'Baz']: {result}");

// This code produces the following output:
// StartsWith ['BAR', 'foo', 'Baz']: True
// StartsWith ['bar', 'foo', 'Baz']: False
// StartsWith ['foo', 'Baz']: False

Exceptions

Type	Condition
ArgumentNullException	first or second is null.

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

Determines whether the beginning of the first sequence is equivalent to the second sequence, using the specified element equality comparer.

Declaration

public static bool StartsWith<T>(this IEnumerable<T> first, IEnumerable<T> second, IEqualityComparer<T>? comparer)

Parameters

Type	Name	Description
IEnumerable<T>	first	The sequence to check.
IEnumerable<T>	second	The sequence to compare to.
IEqualityComparer<T>	comparer	Equality comparer to use.

Returns

Type	Description
bool	true if first begins with elements equivalent to second.

Type Parameters

Name	Description
T	Type of elements.

Remarks

This is the IEnumerable<T> equivalent of StartsWith(string).

This method executes immediately.

Examples

The following code example demonstrates how to check that one sequence starts with the same elements as another sequence using StartsWith.

var sequence = new[]
{
    "BAR",
    "foo",
    "Baz",
    "Qux",
    "BAZ",
    "FOO",
    "bAr",
    "baz",
    "fOo",
    "BaZ",
};

// check that sequence starts with a known sequence of values
var result = sequence
    .StartsWith(new[] { "BAR", "foo", "Baz", }, StringComparer.OrdinalIgnoreCase);

Console.WriteLine($"StartsWith ['BAR', 'foo', 'Baz']: {result}");

result = sequence
    .StartsWith(new[] { "bar", "foo", "Baz", }, StringComparer.OrdinalIgnoreCase);

Console.WriteLine($"StartsWith ['bar', 'foo', 'Baz']: {result}");

result = sequence
    .StartsWith(new[] { "foo", "Baz", }, StringComparer.OrdinalIgnoreCase);

Console.WriteLine($"StartsWith ['foo', 'Baz']: {result}");

// This code produces the following output:
// StartsWith ['BAR', 'foo', 'Baz']: True
// StartsWith ['bar', 'foo', 'Baz']: True
// StartsWith ['foo', 'Baz']: False

Exceptions

Type	Condition
ArgumentNullException	first or second is null.