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Enumerable.ToLookup Method

.NET Framework 4

Creates a generic Lookup<TKey, TElement> from an IEnumerable<T>.

This member is overloaded. For complete information about this member, including syntax, usage, and examples, click a name in the overload list.

Overload List

	Name	Description
	ToLookup<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>)	Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function.
	ToLookup<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>, IEqualityComparer<TKey>)	Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function and key comparer.
	ToLookup<TSource, TKey, TElement>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>)	Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to specified key selector and element selector functions.
	ToLookup<TSource, TKey, TElement>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, IEqualityComparer<TKey>)	Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function, a comparer and an element selector function.

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Reference

Enumerable Class

System.Linq Namespace

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FAQ

ToLookup and multiple enumerations

When you enumerate each group in object returned by ToLookup(), the enumeration happens in-memory. In other words, enumerating each group does not cause re-evaluation of the Linq query. Just like ToArray, this method evaluates the expression once and keeps the results in memory.

History

1/19/2012
Shital Shah