Method CountBy
CountBy<TSource, TKey>(IAsyncEnumerable<TSource>, Func<TSource, TKey>)
Applies a key-generating function to each element of a sequence and returns a sequence of unique keys and their number of occurrences in the original sequence.
Declaration
public static IAsyncEnumerable<KeyValuePair<TKey, int>> CountBy<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 transforms each item of source sequence into a key to be compared against the others. |
Returns
| Type | Description |
|---|---|
| IAsyncEnumerable<KeyValuePair<TKey, int>> | A sequence of unique keys and their number of occurrences in the original sequence. |
Type Parameters
| Name | Description |
|---|---|
| TSource | Type of the elements of the source sequence. |
| TKey | Type of the projected element. |
CountBy<TSource, TKey>(IAsyncEnumerable<TSource>, Func<TSource, TKey>, IEqualityComparer<TKey>?)
Applies a key-generating function to each element of a sequence and returns a sequence of unique keys and their number of occurrences in the original sequence. An additional argument specifies a comparer to use for testing equivalence of keys.
Declaration
public static IAsyncEnumerable<KeyValuePair<TKey, int>> CountBy<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 transforms each item of source sequence into a key to be compared against the others. |
| 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<KeyValuePair<TKey, int>> | A sequence of unique keys and their number of occurrences in the original sequence. |
Type Parameters
| Name | Description |
|---|---|
| TSource | Type of the elements of the source sequence. |
| TKey | Type of the projected element. |