Method GroupAdjacent

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

Groups the adjacent elements of a sequence according to a specified key selector function.

Declaration
public static IEnumerable<IGrouping<TKey, TSource>> GroupAdjacent<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
Parameters
Type Name Description
IEnumerable<TSource> source

A sequence whose elements to group.
Func<TSource, TKey> keySelector

A function to extract the key for each element.
Returns
Type Description
IEnumerable<IGrouping<TKey, TSource>>

A sequence of groupings where each grouping (IGrouping<TKey, TElement>) contains the key and the adjacent elements in the same order as found in the source sequence.
Type Parameters
Name Description
TSource

The type of the elements of source.
TKey

The type of the key returned by keySelector.
Remarks

This method is implemented by using deferred execution and streams the groupings. The grouping elements, however, are buffered. Each grouping is therefore yielded as soon as it is complete and before the next grouping occurs.

Examples

The following code example shows how to group adjacent items in a sequence using GroupAdjacent:

var sequence = new[]
{
    (key: 1, value: 123),
    (key: 1, value: 456),
    (key: 1, value: 789),
    (key: 2, value: 987),
    (key: 2, value: 654),
    (key: 2, value: 321),
    (key: 3, value: 789),
    (key: 3, value: 456),
    (key: 3, value: 123),
    (key: 1, value: 123),
    (key: 1, value: 456),
    (key: 1, value: 781),
};

// Group adjacent items
var result = sequence
    .GroupAdjacent(
        x => x.key);

Console.WriteLine(
    "[ " + 
    string.Join(
        ", ", 
        result.Select(c => "[" + string.Join(", ", c) + "]")) +
    " ]");

// This code produces the following output:
// [ [(1, 123), (1, 456), (1, 789)], [(2, 987), (2, 654), (2, 321)], [(3, 789), (3, 456), (3, 123)], [(1, 123), (1, 456), (1, 781)] ]
Exceptions
Type Condition
ArgumentNullException

source or keySelector is null.
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GroupAdjacent<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>, IEqualityComparer<TKey>?)

Groups the adjacent elements of a sequence according to a specified key selector function and compares the keys by using a specified comparer.

Declaration
public static IEnumerable<IGrouping<TKey, TSource>> GroupAdjacent<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? comparer)
Parameters
Type Name Description
IEnumerable<TSource> source

A sequence whose elements to group.
Func<TSource, TKey> keySelector

A function to extract the key for each element.
IEqualityComparer<TKey> comparer

An IEqualityComparer<T> to compare keys.
Returns
Type Description
IEnumerable<IGrouping<TKey, TSource>>

A sequence of groupings where each grouping (IGrouping<TKey, TElement>) contains the key and the adjacent elements in the same order as found in the source sequence.
Type Parameters
Name Description
TSource

The type of the elements of source.
TKey

The type of the key returned by keySelector.
Remarks

This method is implemented by using deferred execution and streams the groupings. The grouping elements, however, are buffered. Each grouping is therefore yielded as soon as it is complete and before the next grouping occurs.

Examples

The following code example shows how to group adjacent items in a sequence using GroupAdjacent:

var sequence = new[]
{
    (key: "jan", value: 123),
    (key: "Jan", value: 456),
    (key: "JAN", value: 789),
    (key: "feb", value: 987),
    (key: "Feb", value: 654),
    (key: "FEB", value: 321),
    (key: "mar", value: 789),
    (key: "Mar", value: 456),
    (key: "MAR", value: 123),
    (key: "jan", value: 123),
    (key: "Jan", value: 456),
    (key: "JAN", value: 781),
};

// Group adjacent items
var result = sequence
    .GroupAdjacent(
        x => x.key, 
        StringComparer.OrdinalIgnoreCase);

Console.WriteLine(
    "[ " + 
    string.Join(
        ", ", 
        result.Select(c => "[" + string.Join(", ", c) + "]")) +
    " ]");

// This code produces the following output:
// [ [(jan, 123), (Jan, 456), (JAN, 789)], [(feb, 987), (Feb, 654), (FEB, 321)], [(mar, 789), (Mar, 456), (MAR, 123)], [(jan, 123), (Jan, 456), (JAN, 781)] ]
Exceptions
Type Condition
ArgumentNullException

source or keySelector is null.
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GroupAdjacent<TSource, TKey, TElement>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>)

Groups the adjacent elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function.

Declaration
public static IEnumerable<IGrouping<TKey, TElement>> GroupAdjacent<TSource, TKey, TElement>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector)
Parameters
Type Name Description
IEnumerable<TSource> source

A sequence whose elements to group.
Func<TSource, TKey> keySelector

A function to extract the key for each element.
Func<TSource, TElement> elementSelector

A function to map each source element to an element in the resulting grouping.
Returns
Type Description
IEnumerable<IGrouping<TKey, TElement>>

A sequence of groupings where each grouping (IGrouping<TKey, TElement>) contains the key and the adjacent elements (of type TElement) in the same order as found in the source sequence.
Type Parameters
Name Description
TSource

The type of the elements of source.
TKey

The type of the key returned by keySelector.
TElement

The type of the elements in the resulting groupings.
Remarks

This method is implemented by using deferred execution and streams the groupings. The grouping elements, however, are buffered. Each grouping is therefore yielded as soon as it is complete and before the next grouping occurs.

Examples

The following code example shows how to group adjacent items in a sequence using GroupAdjacent:

var sequence = new[]
{
    (key: 1, value: 123),
    (key: 1, value: 456),
    (key: 1, value: 789),
    (key: 2, value: 987),
    (key: 2, value: 654),
    (key: 2, value: 321),
    (key: 3, value: 789),
    (key: 3, value: 456),
    (key: 3, value: 123),
    (key: 1, value: 123),
    (key: 1, value: 456),
    (key: 1, value: 781),
};

// Group adjacent items
var result = sequence
    .GroupAdjacent(
        x => x.key,
        x => x.value);

Console.WriteLine(
    "[ " + 
    string.Join(
        ", ", 
        result.Select(c => "[" + string.Join(", ", c) + "]")) +
    " ]");

// This code produces the following output:
// [ [(1, 123), (1, 456), (1, 789)], [(2, 987), (2, 654), (2, 321)], [(3, 789), (3, 456), (3, 123)], [(1, 123), (1, 456), (1, 781)] ]
Exceptions
Type Condition
ArgumentNullException

source, keySelector, or elementSelector is null.
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GroupAdjacent<TSource, TKey, TElement>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, IEqualityComparer<TKey>?)

Groups the adjacent elements of a sequence according to a specified key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function.

Declaration
public static IEnumerable<IGrouping<TKey, TElement>> GroupAdjacent<TSource, TKey, TElement>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey>? comparer)
Parameters
Type Name Description
IEnumerable<TSource> source

A sequence whose elements to group.
Func<TSource, TKey> keySelector

A function to extract the key for each element.
Func<TSource, TElement> elementSelector

A function to map each source element to an element in the resulting grouping.
IEqualityComparer<TKey> comparer

An IEqualityComparer<T> to compare keys.
Returns
Type Description
IEnumerable<IGrouping<TKey, TElement>>

A sequence of groupings where each grouping (IGrouping<TKey, TElement>) contains the key and the adjacent elements (of type TElement) in the same order as found in the source sequence.
Type Parameters
Name Description
TSource

The type of the elements of source.
TKey

The type of the key returned by keySelector.
TElement

The type of the elements in the resulting groupings.
Remarks

This method is implemented by using deferred execution and streams the groupings. The grouping elements, however, are buffered. Each grouping is therefore yielded as soon as it is complete and before the next grouping occurs.

Examples

The following code example shows how to group adjacent items in a sequence using GroupAdjacent:

var sequence = new[]
{
    (key: "jan", value: 123),
    (key: "Jan", value: 456),
    (key: "JAN", value: 789),
    (key: "feb", value: 987),
    (key: "Feb", value: 654),
    (key: "FEB", value: 321),
    (key: "mar", value: 789),
    (key: "Mar", value: 456),
    (key: "MAR", value: 123),
    (key: "jan", value: 123),
    (key: "Jan", value: 456),
    (key: "JAN", value: 781),
};

// Group adjacent items
var result = sequence
    .GroupAdjacent(
        x => x.key,
        x => x.value,
        StringComparer.OrdinalIgnoreCase);

Console.WriteLine(
    "[ " + 
    string.Join(
        ", ", 
        result.Select(c => "[" + string.Join(", ", c) + "]")) +
    " ]");

// This code produces the following output:
// [ [123, 456, 789], [987, 654, 321], [789, 456, 123], [123, 456, 781] ]
Exceptions
Type Condition
ArgumentNullException

source, keySelector, or elementSelector is null.

GroupAdjacent<TSource, TKey, TResult>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TKey, IReadOnlyList<TSource>, TResult>)

Groups the adjacent elements of a sequence according to a specified key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function.

Declaration
public static IEnumerable<TResult> GroupAdjacent<TSource, TKey, TResult>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, IReadOnlyList<TSource>, TResult> resultSelector)
Parameters
Type Name Description
IEnumerable<TSource> source

A sequence whose elements to group.
Func<TSource, TKey> keySelector

A function to extract the key for each element.
Func<TKey, IReadOnlyList<TSource>, TResult> resultSelector

A function to map each key and associated source elements to a result object.
Returns
Type Description
IEnumerable<TResult>

A collection of elements of type TResult where each element represents a projection over a group and its key.
Type Parameters
Name Description
TSource

The type of the elements of source.
TKey

The type of the key returned by keySelector.
TResult

The type of the elements in the resulting sequence.
Remarks

This method is implemented by using deferred execution and streams the groupings. The grouping elements, however, are buffered. Each grouping is therefore yielded as soon as it is complete and before the next grouping occurs.

Exceptions
Type Condition
ArgumentNullException

source, keySelector, or resultSelector is null.

GroupAdjacent<TSource, TKey, TResult>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TKey, IReadOnlyList<TSource>, TResult>, IEqualityComparer<TKey>?)

Groups the adjacent elements of a sequence according to a specified key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function.

Declaration
public static IEnumerable<TResult> GroupAdjacent<TSource, TKey, TResult>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, IReadOnlyList<TSource>, TResult> resultSelector, IEqualityComparer<TKey>? comparer)
Parameters
Type Name Description
IEnumerable<TSource> source

A sequence whose elements to group.
Func<TSource, TKey> keySelector

A function to extract the key for each element.
Func<TKey, IReadOnlyList<TSource>, TResult> resultSelector

A function to map each key and associated source elements to a result object.
IEqualityComparer<TKey> comparer

An IEqualityComparer<T> to compare keys.
Returns
Type Description
IEnumerable<TResult>

A collection of elements of type TResult where each element represents a projection over a group and its key.
Type Parameters
Name Description
TSource

The type of the elements of source.
TKey

The type of the key returned by keySelector.
TResult

The type of the elements in the resulting sequence.
Remarks

This method is implemented by using deferred execution and streams the groupings. The grouping elements, however, are buffered. Each grouping is therefore yielded as soon as it is complete and before the next grouping occurs.

Exceptions
Type Condition
ArgumentNullException

source, keySelector, or resultSelector is null.