Method IndexBy
View SourceIndexBy<TSource, TKey>(IAsyncEnumerable<TSource>, Func<TSource, TKey>)
Applies a key-generating function to each element of a sequence and returns a sequence that contains the elements of the original sequence as well its key and index inside the group of its key.
Declaration
public static IAsyncEnumerable<(int index, TSource item)> IndexBy<TSource, TKey>(this IAsyncEnumerable<TSource> source, Func<TSource, TKey> keySelector)Parameters
| Type | Name | Description |
|---|---|---|
| IAsyncEnumerable<TSource> | source | Source sequence. |
| Func<TSource, TKey> | keySelector | Function that projects the key given an element in the source sequence. |
Returns
| Type | Description |
|---|---|
| IAsyncEnumerable<(int index, TSource item)> | A sequence of elements paired with their index within the key-group. The index is the key and the element is the value of the pair. |
Type Parameters
| Name | Description |
|---|---|
| TSource | Type of the source sequence elements. |
| TKey | Type of the projected key. |
Exceptions
| Type | Condition |
|---|---|
| ArgumentNullException |
|
| ArgumentNullException |
|
IndexBy<TSource, TKey>(IAsyncEnumerable<TSource>, Func<TSource, TKey>, IEqualityComparer<TKey>?)
Applies a key-generating function to each element of a sequence and returns a sequence that contains the elements of the original sequence as well its key and index inside the group of its key. An additional parameter specifies a comparer to use for testing the equivalence of keys.
Declaration
public static IAsyncEnumerable<(int index, TSource item)> IndexBy<TSource, TKey>(this IAsyncEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? comparer)Parameters
| Type | Name | Description |
|---|---|---|
| IAsyncEnumerable<TSource> | source | Source sequence. |
| Func<TSource, TKey> | keySelector | Function that projects the key given an element in the source sequence. |
| IEqualityComparer<TKey> | comparer | The equality comparer to use to determine whether or not keys are
equal. If null, the default equality comparer for
|
Returns
| Type | Description |
|---|---|
| IAsyncEnumerable<(int index, TSource item)> | A sequence of elements paired with their index within the key-group. The index is the key and the element is the value of the pair. |
Type Parameters
| Name | Description |
|---|---|
| TSource | Type of the source sequence elements. |
| TKey | Type of the projected key. |
Exceptions
| Type | Condition |
|---|---|
| ArgumentNullException |
|
| ArgumentNullException |
|