Method ThenBy

ThenBy<T, TKey>(IOrderedEnumerable<T>, Func<T, TKey>, OrderByDirection)

Performs a subsequent ordering of elements of a sequence in a particular direction (ascending, descending) according to a key

Declaration

public static IOrderedEnumerable<T> ThenBy<T, TKey>(this IOrderedEnumerable<T> source, Func<T, TKey> keySelector, OrderByDirection direction)

Parameters

Type	Name	Description
IOrderedEnumerable<T>	source	The sequence to order
Func<T, TKey>	keySelector	A key selector function
OrderByDirection	direction	A direction in which to order the elements (ascending, descending)

Returns

Type	Description
IOrderedEnumerable<T>	An ordered copy of the source sequence

Type Parameters

Name	Description
T	The type of the elements in the source sequence
TKey	The type of the key used to order elements

Remarks

This method is implemented by using deferred execution. However, source will be consumed in it's entirety immediately when first element of the returned sequence is consumed.

Examples

The following code example demonstrates how to sort a sequence using OrderBy and ThenBy.

var fruits = new[]
{
    "grape", "passionfruit", "banana", "Mango",
    "Orange", "raspberry", "apple", "blueberry",
};

// Sort the strings first by their length and then
// alphabetically by passing the identity selector function.
var result = fruits
    .OrderBy(fruit => fruit.Length)
    .ThenBy(fruit => fruit);

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

// This code produces the following output:
// [apple, grape, Mango, banana, Orange, blueberry, raspberry, passionfruit]

Exceptions

Type	Condition
ArgumentNullException	source or keySelector is null.

ThenBy<T, TKey>(IOrderedEnumerable<T>, Func<T, TKey>, IComparer<TKey>?, OrderByDirection)

Performs a subsequent ordering of elements of a sequence in a particular direction (ascending, descending) according to a key

Declaration

public static IOrderedEnumerable<T> ThenBy<T, TKey>(this IOrderedEnumerable<T> source, Func<T, TKey> keySelector, IComparer<TKey>? comparer, OrderByDirection direction)

Parameters

Type	Name	Description
IOrderedEnumerable<T>	source	The sequence to order
Func<T, TKey>	keySelector	A key selector function
IComparer<TKey>	comparer	An IComparer<T> to compare keys
OrderByDirection	direction	A direction in which to order the elements (ascending, descending)

Returns

Type	Description
IOrderedEnumerable<T>	An ordered copy of the source sequence

Type Parameters

Name	Description
T	The type of the elements in the source sequence
TKey	The type of the key used to order elements

Remarks

This method is implemented by using deferred execution. However, source will be consumed in it's entirety immediately when first element of the returned sequence is consumed.

Examples

The following code example demonstrates how to sort a sequence using OrderBy and ThenBy.

var fruits = new[]
{
    "grape", "passionfruit", "banana", "Mango",
    "Orange", "raspberry", "apple", "blueberry",
};

// Sort the strings first by their length and then
// alphabetically by passing the identity selector function.
var result = fruits
    .OrderBy(fruit => fruit.Length)
    .ThenBy(fruit => fruit, StringComparer.Ordinal);

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

// This code produces the following output:
// [Mango, apple, grape, Orange, banana, blueberry, raspberry, passionfruit]

Exceptions

Type	Condition
ArgumentNullException	source or keySelector is null.