ToDictionary
suggest changeThe ToDictionary()
LINQ method can be used to generate a Dictionary<TKey, TElement>
collection based on a given IEnumerable<T>
source.
IEnumerable<User> users = GetUsers();
Dictionary<int, User> usersById = users.ToDictionary(x => x.Id);
In this example, the single argument passed to ToDictionary
is of type Func<TSource, TKey>
, which returns the key for each element.
This is a concise way to perform the following operation:
Dictionary<int, User> usersById = new Dictionary<int User>();
foreach (User u in users)
{
usersById.Add(u.Id, u);
}
You can also pass a second parameter to the ToDictionary
method, which is of type Func<TSource, TElement>
and returns the Value
to be added for each entry.
IEnumerable<User> users = GetUsers();
Dictionary<int, string> userNamesById = users.ToDictionary(x => x.Id, x => x.Name);
It is also possible to specify the IComparer
that is used to compare key values. This can be useful when the key is a string and you want it to match case-insensitive.
IEnumerable<User> users = GetUsers();
Dictionary<string, User> usersByCaseInsenstiveName = users.ToDictionary(x => x.Name, StringComparer.InvariantCultureIgnoreCase);
var user1 = usersByCaseInsenstiveName["john"];
var user2 = usersByCaseInsenstiveName["JOHN"];
user1 == user2; // Returns true
Note: the ToDictionary
method requires all keys to be unique, there must be no duplicate keys. If there are, then an exception is thrown: ArgumentException: An item with the same key has already been added.
If you have a scenario where you know that you will have multiple elements with the same key, then you are better off using ToLookup
instead.