Method TagFirstLast

TagFirstLast<TSource>(IEnumerable<TSource>)

Returns a sequence of tuples containing the element and flags indicating whether the element is the first and/or last of the sequence.

Declaration

public static IEnumerable<(TSource item, bool isFirst, bool isLast)> TagFirstLast<TSource>(this IEnumerable<TSource> source)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.

Returns

Type	Description
IEnumerable<(TSource item, bool isFirst, bool isLast)>	Returns the resulting sequence.

Type Parameters

Name	Description
TSource	The type of the elements of source.

Remarks

This operator uses deferred execution and streams its results.

Examples

The following code example demonstrates how tag elements of a sequence with information on whether it is the first or last element of the sequence using TagFirstLast.

var sequence = Enumerable.Range(1, 4);

// Replace a value in a sequence
var result = sequence
    .TagFirstLast();

Console.WriteLine(
    "[" +
    string.Join(", ", result) +
    "]");

// This code produces the following output:
// [(1, True, False), (2, False, False), (3, False, False), (4, False, True)]

Exceptions

Type	Condition
ArgumentNullException	source is null.

TagFirstLast<TSource, TResult>(IEnumerable<TSource>, Func<TSource, bool, bool, TResult>)

Returns a sequence resulting from applying a function to each element in the source sequence with additional parameters indicating whether the element is the first and/or last of the sequence.

Declaration

public static IEnumerable<TResult> TagFirstLast<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, bool, bool, TResult> resultSelector)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.
Func<TSource, bool, bool, TResult>	resultSelector	A function that determines how to project the each element along with its first or last tag.

Returns

Type	Description
IEnumerable<TResult>	Returns the resulting sequence.

Type Parameters

Name	Description
TSource	The type of the elements of source.
TResult	The type of the element of the returned sequence.

Remarks

This operator uses deferred execution and streams its results.

Examples

The following code example demonstrates how tag elements of a sequence with information on whether it is the first or last element of the sequence using TagFirstLast.

var sequence = Enumerable.Range(1, 4);

// Replace a value in a sequence
var result = sequence
    .TagFirstLast(
        (item, first, last) => new 
        { 
            Item = item, 
            IsEdge = first || last, 
        });

Console.WriteLine(
    "[" +
    string.Join(", ", result) +
    "]");

// This code produces the following output:
// [{ Item = 1, IsEdge = True }, { Item = 2, IsEdge = False }, { Item = 3, IsEdge = False }, { Item = 4, IsEdge = True }]

Exceptions

Type	Condition
ArgumentNullException	source or resultSelector is null.