Queryable.CountBy<TSource,TKey> Method
Definition
Important
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Returns the count of each element from a sequence according to a specified key selector function.
public static System.Linq.IQueryable<System.Collections.Generic.KeyValuePair<TKey,int>> CountBy<TSource,TKey> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,TKey>> keySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = default);static member CountBy : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, 'Key>> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Linq.IQueryable<System.Collections.Generic.KeyValuePair<'Key, int>><Extension()>
Public Function CountBy(Of TSource, TKey) (source As IQueryable(Of TSource), keySelector As Expression(Of Func(Of TSource, TKey)), Optional comparer As IEqualityComparer(Of TKey) = Nothing) As IQueryable(Of KeyValuePair(Of TKey, Integer))Type Parameters
- TSource
The type of the elements of source.
- TKey
The type of key to distinguish elements by.
Parameters
- source
- IQueryable<TSource>
The sequence to count elements from.
- keySelector
- Expression<Func<TSource,TKey>>
A function to extract the key for each element.
- comparer
- IEqualityComparer<TKey>
An IEqualityComparer<T> to compare keys.
Returns
An IQueryable<T> that contains count for each distinct elements from the source sequence as a KeyValuePair<TKey,TValue> object.
Exceptions
source is null.
Applies to
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