Method StartsWith

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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.
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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.