,System.Func{--0,--1})} ,System.Func{--0,--1},System.Collections.Generic.IEqualityComparer{--1})} ,System.Func{--0,--1},System.Func{--0,--2})} ,System.Func{--0,--1},System.Func{--0,--2},System.Collections.Generic.IEqualityComparer{--1})}

Observable.ToLookup(IObservable, Func) method¶

Defined in

Type: Observable Namespace: System.Reactive.Linq Assembly: System.Reactive.dll

Applies to

netstandard2.0

Overloads¶

1. public static IObservable<ILookup<TKey, TSource>> ToLookup<TSource, TKey>(this IObservable<TSource> source, Func<TSource, TKey> keySelector)
2. public static IObservable<ILookup<TKey, TSource>> ToLookup<TSource, TKey>(this IObservable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)
3. public static IObservable<ILookup<TKey, TElement>> ToLookup<TSource, TKey, TElement>(this IObservable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector)
4. public static IObservable<ILookup<TKey, TElement>> ToLookup<TSource, TKey, TElement>(this IObservable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey> comparer)

1. Overload¶

public static IObservable<ILookup<TKey, TSource>> ToLookup<TSource, TKey>(this IObservable<TSource> source, Func<TSource, TKey> keySelector)

Summary: Creates a lookup from an observable sequence according to a specified key selector function.

Type parameters

Name	Description
`TSource`	The type of the elements in the source sequence.
`TKey`	The type of the lookup key computed for each element in the source sequence.

Parameters

Name	Type	Description
`source`	IObservable	An observable sequence to create a lookup for.
`keySelector`	Func	A function to extract a key from each element.

Returns: IObservable> -- An observable sequence containing a single element with a lookup mapping unique key values onto the corresponding source sequence's elements.

Remarks

The return type of this operator differs from the corresponding operator on IEnumerable in order to retain asynchronous behavior.

Exceptions

Type	Condition
System.ArgumentNullException	`source` or `keySelector` is null.

2. Overload¶

public static IObservable<ILookup<TKey, TSource>> ToLookup<TSource, TKey>(this IObservable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer)

Summary: Creates a lookup from an observable sequence according to a specified key selector function, and a comparer.

Type parameters

Name	Description
`TSource`	The type of the elements in the source sequence.
`TKey`	The type of the lookup key computed for each element in the source sequence.

Parameters

Name	Type	Description
`source`	IObservable	An observable sequence to create a lookup for.
`keySelector`	Func	A function to extract a key from each element.
`comparer`	IEqualityComparer	An equality comparer to compare keys.

Returns: IObservable> -- An observable sequence containing a single element with a lookup mapping unique key values onto the corresponding source sequence's elements.

Remarks

The return type of this operator differs from the corresponding operator on IEnumerable in order to retain asynchronous behavior.

Exceptions

Type	Condition
System.ArgumentNullException	`source` or `keySelector` or `comparer` is null.

3. Overload¶

public static IObservable<ILookup<TKey, TElement>> ToLookup<TSource, TKey, TElement>(this IObservable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector)

Summary: Creates a lookup from an observable sequence according to a specified key selector function, and an element selector function.

Type parameters

Name	Description
`TSource`	The type of the elements in the source sequence.
`TKey`	The type of the lookup key computed for each element in the source sequence.
`TElement`	The type of the lookup value computed for each element in the source sequence.

Parameters

Name	Type	Description
`source`	IObservable	An observable sequence to create a lookup for.
`keySelector`	Func	A function to extract a key from each element.
`elementSelector`	Func	A transform function to produce a result element value from each element.

Returns: IObservable> -- An observable sequence containing a single element with a lookup mapping unique key values onto the corresponding source sequence's elements.

Remarks

The return type of this operator differs from the corresponding operator on IEnumerable in order to retain asynchronous behavior.

Exceptions

Type	Condition
System.ArgumentNullException	`source` or `keySelector` or `elementSelector` is null.

4. Overload¶

public static IObservable<ILookup<TKey, TElement>> ToLookup<TSource, TKey, TElement>(this IObservable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey> comparer)

Summary: Creates a lookup from an observable sequence according to a specified key selector function, a comparer, and an element selector function.

Type parameters

Name	Description
`TSource`	The type of the elements in the source sequence.
`TKey`	The type of the lookup key computed for each element in the source sequence.
`TElement`	The type of the lookup value computed for each element in the source sequence.

Parameters

Name	Type	Description
`source`	IObservable	An observable sequence to create a lookup for.
`keySelector`	Func	A function to extract a key from each element.
`elementSelector`	Func	A transform function to produce a result element value from each element.
`comparer`	IEqualityComparer	An equality comparer to compare keys.

Returns: IObservable> -- An observable sequence containing a single element with a lookup mapping unique key values onto the corresponding source sequence's elements.

Remarks

The return type of this operator differs from the corresponding operator on IEnumerable in order to retain asynchronous behavior.

Exceptions

Type	Condition
System.ArgumentNullException	`source` or `keySelector` or `elementSelector` or `comparer` is null.