Method ThenBy

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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.
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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.