Method ScanBy

ScanBy<TSource, TKey, TState>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TKey, TState>, Func<TState, TKey, TSource, TState>)

Applies an accumulator function over sequence element keys, returning the keys along with intermediate accumulator states.

Declaration

public static IEnumerable<(TKey key, TState state)> ScanBy<TSource, TKey, TState>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, TState> seedSelector, Func<TState, TKey, TSource, TState> accumulator)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.
Func<TSource, TKey>	keySelector	A function that returns the key given an element.
Func<TKey, TState>	seedSelector	A function to determine the initial value for the accumulator that is invoked once per key encountered.
Func<TState, TKey, TSource, TState>	accumulator	An accumulator function invoked for each element.

Returns

Type	Description
IEnumerable<(TKey key, TState state)>	A sequence of keys paired with intermediate accumulator states.

Type Parameters

Name	Description
TSource	Type of the elements of the source sequence.
TKey	The type of the key.
TState	Type of the state.

Remarks

This operator uses deferred execution and streams its result.

Examples

The following code example demonstrates how to execute a post-fix scan by key on a sequence using ScanBy.

var sequence = Enumerable.Range(1, 10);

// execute a scan of the sequence
var result = sequence
    .ScanBy(
        x => x % 2,
        k => k * 1000,
        (a, k, b) => a + b);

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

// This code produces the following output:
// [(1, 1001), (0, 2), (1, 1004), (0, 6), (1, 1009), (0, 12), (1, 1016), (0, 20), (1, 1025), (0, 30)]

Exceptions

Type	Condition
ArgumentNullException	source, keySelector, seedSelector, or accumulator is null.

ScanBy<TSource, TKey, TState>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TKey, TState>, Func<TState, TKey, TSource, TState>, IEqualityComparer<TKey>?)

Applies an accumulator function over sequence element keys, returning the keys along with intermediate accumulator states.

Declaration

public static IEnumerable<(TKey key, TState state)> ScanBy<TSource, TKey, TState>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, TState> seedSelector, Func<TState, TKey, TSource, TState> accumulator, IEqualityComparer<TKey>? comparer)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The source sequence.
Func<TSource, TKey>	keySelector	A function that returns the key given an element.
Func<TKey, TState>	seedSelector	A function to determine the initial value for the accumulator that is invoked once per key encountered.
Func<TState, TKey, TSource, TState>	accumulator	An accumulator function invoked for each element.
IEqualityComparer<TKey>	comparer	The equality comparer to use to determine whether or not keys are equal. If null, the default equality comparer for TSource is used.

Returns

Type	Description
IEnumerable<(TKey key, TState state)>	A sequence of keys paired with intermediate accumulator states.

Type Parameters

Name	Description
TSource	Type of the elements of the source sequence.
TKey	The type of the key.
TState	Type of the state.

Remarks

This operator uses deferred execution and streams its result.

Examples

The following code example demonstrates how to execute a post-fix scan by key on a sequence using ScanBy.

var sequence = new[]
{
    "BAR",
    "foo",
    "Baz",
    "Qux",
    "BAZ",
    "FOO",
    "bAr",
    "baz",
    "fOo",
    "BaZ",
};

// execute a scan of the sequence
var result = sequence
    .ScanBy(
        x => x[..1],
        k => 0,
        (a, k, b) => a + 1,
        StringComparer.OrdinalIgnoreCase);

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

// This code produces the following output:
// [(B, 1), (f, 1), (B, 2), (Q, 1), (B, 3), (F, 2), (b, 4), (b, 5), (f, 3), (B, 6)]

Exceptions

Type	Condition
ArgumentNullException	source, keySelector, seedSelector, or accumulator is null.