Method PartialSortBy

PartialSortBy<TSource, TKey>(IEnumerable<TSource>, int, Func<TSource, TKey>)

Executes a partial sort of the top count elements of a sequence according to the key for each element. If count is less than the total number of elements in source, then this method will improve performance.

Declaration

public static IEnumerable<TSource> PartialSortBy<TSource, TKey>(this IEnumerable<TSource> source, int count, Func<TSource, TKey> keySelector)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.
int	count	Number of (maximum) elements to return.
Func<TSource, TKey>	keySelector	A function to extract a key from an element.

Returns

Type	Description
IEnumerable<TSource>	A sequence containing at most top count elements from source, in ascending order of their keys.

Type Parameters

Name	Description
TSource	Type of elements in the sequence.
TKey	Type of keys.

Remarks

This operation is an O(n * log(K)) where K is count.

This operator uses deferred execution and streams it results.

Examples

The following code example demonstrates how to get the top N items of a sequence using PartialSort.

var sequence = new[]
{
    (key: 5, text: "1"),
    (key: 5, text: "2"),
    (key: 4, text: "3"),
    (key: 4, text: "4"),
    (key: 3, text: "5"),
    (key: 3, text: "6"),
    (key: 2, text: "7"),
    (key: 2, text: "8"),
    (key: 1, text: "9"),
    (key: 1, text: "10"),
};

// Get the top N items
var result = sequence
    .PartialSortBy(
        3,
        x => x.key);

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

// This code produces the following output:
// [(1, 9), (1, 10), (2, 7)]

Exceptions

Type	Condition
ArgumentNullException	source or keySelector is null.
ArgumentOutOfRangeException	count is less than 1.

PartialSortBy<TSource, TKey>(IEnumerable<TSource>, int, Func<TSource, TKey>, OrderByDirection)

Executes a direction partial sort of the top count elements of a sequence according to the key for each element. If count is less than the total number of elements in source, then this method will improve performance.

Declaration

public static IEnumerable<TSource> PartialSortBy<TSource, TKey>(this IEnumerable<TSource> source, int count, Func<TSource, TKey> keySelector, OrderByDirection direction)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.
int	count	Number of (maximum) elements to return.
Func<TSource, TKey>	keySelector	A function to extract a key from an element.
OrderByDirection	direction	The direction in which to sort the elements

Returns

Type	Description
IEnumerable<TSource>	A sequence containing at most top count elements from source, in the specified order of their keys.

Type Parameters

Name	Description
TSource	Type of elements in the sequence.
TKey	Type of keys.

Remarks

This operation is an O(n * log(K)) where K is count.

This operator uses deferred execution and streams it results.

Examples

The following code example demonstrates how to get the top N items of a sequence using PartialSort.

var sequence = new[]
{
    (key: 5, text: "1"),
    (key: 5, text: "2"),
    (key: 4, text: "3"),
    (key: 4, text: "4"),
    (key: 3, text: "5"),
    (key: 3, text: "6"),
    (key: 2, text: "7"),
    (key: 2, text: "8"),
    (key: 1, text: "9"),
    (key: 1, text: "10"),
};

// Get the top N items
var result = sequence
    .PartialSortBy(
        3,
        x => x.key,
        OrderByDirection.Descending);

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

// This code produces the following output:
// [(5, 1), (5, 2), (4, 3)]

Exceptions

Type	Condition
ArgumentNullException	source or keySelector is null.
ArgumentOutOfRangeException	count is less than 1.

PartialSortBy<TSource, TKey>(IEnumerable<TSource>, int, Func<TSource, TKey>, IComparer<TKey>?)

Executes a partial sort of the top count elements of a sequence according to the key for each element, using comparer to compare the keys. If count is less than the total number of elements in source, then this method will improve performance.

Declaration

public static IEnumerable<TSource> PartialSortBy<TSource, TKey>(this IEnumerable<TSource> source, int count, Func<TSource, TKey> keySelector, IComparer<TKey>? comparer)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.
int	count	Number of (maximum) elements to return.
Func<TSource, TKey>	keySelector	A function to extract a key from an element.
IComparer<TKey>	comparer	A IComparer<T> to compare elements.

Returns

Type	Description
IEnumerable<TSource>	A sequence containing at most top count elements from source, in ascending order of their keys.

Type Parameters

Name	Description
TSource	Type of elements in the sequence.
TKey	Type of keys.

Remarks

This operation is an O(n * log(K)) where K is count.

This operator uses deferred execution and streams it results.

Examples

The following code example demonstrates how to get the top N items of a sequence using PartialSort.

var sequence = new[]
{
    (key: 5, text: "1"),
    (key: 5, text: "2"),
    (key: 4, text: "3"),
    (key: 4, text: "4"),
    (key: 3, text: "5"),
    (key: 3, text: "6"),
    (key: 2, text: "7"),
    (key: 2, text: "8"),
    (key: 1, text: "9"),
    (key: 1, text: "10"),
};

// Get the top N items
var result = sequence
    .PartialSortBy(
        1,
        x => x.key,
        Comparer<int>.Create((x, y) => (x % 2).CompareTo(y % 2)));

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

// This code produces the following output:
// [(4, 3)]

Exceptions

Type	Condition
ArgumentNullException	source or keySelector is null.
ArgumentOutOfRangeException	count is less than 1.

PartialSortBy<TSource, TKey>(IEnumerable<TSource>, int, Func<TSource, TKey>, IComparer<TKey>?, OrderByDirection)

Executes a direction partial sort of the top count elements of a sequence according to the key for each element, using comparer to compare the keys. If count is less than the total number of elements in source, then this method will improve performance.

Declaration

public static IEnumerable<TSource> PartialSortBy<TSource, TKey>(this IEnumerable<TSource> source, int count, Func<TSource, TKey> keySelector, IComparer<TKey>? comparer, OrderByDirection direction)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.
int	count	Number of (maximum) elements to return.
Func<TSource, TKey>	keySelector	A function to extract a key from an element.
IComparer<TKey>	comparer	A IComparer<T> to compare elements.
OrderByDirection	direction	The direction in which to sort the elements

Returns

Type	Description
IEnumerable<TSource>	A sequence containing at most top count elements from source, in the specified order of their keys.

Type Parameters

Name	Description
TSource	Type of elements in the sequence.
TKey	Type of keys.

Remarks

This operation is an O(n * log(K)) where K is count.

This operator uses deferred execution and streams it results.

Examples

The following code example demonstrates how to get the top N items of a sequence using PartialSort.

var sequence = new[]
{
    (key: 5, text: "1"),
    (key: 5, text: "2"),
    (key: 4, text: "3"),
    (key: 4, text: "4"),
    (key: 3, text: "5"),
    (key: 3, text: "6"),
    (key: 2, text: "7"),
    (key: 2, text: "8"),
    (key: 1, text: "9"),
    (key: 1, text: "10"),
};

// Get the top N items
var result = sequence
    .PartialSortBy(
        1,
        x => x.key,
        Comparer<int>.Create((x, y) => (x % 2).CompareTo(y % 2)),
        OrderByDirection.Descending);

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

// This code produces the following output:
// [(5, 1), (5, 2), (3, 5), (3, 6), (1, 9), (1, 10)]

Exceptions

Type	Condition
ArgumentNullException	source or keySelector is null.
ArgumentOutOfRangeException	count is less than 1.