CODEWITHSUNDEEP
c#listdictionary
user1240679
user1240679

Reputation: 6979

Lambda expression in ToDictionary

To convert a list to a dictionary, we can do it easily with the follwing:

list.ToDictionary(v=> v, v=>true);

For the first parameter in ToDictionary, I can understand the first parameter is the element of the dictionary. But what is meant by v=> true?

The second parameter should be of the type IEqualityComparer. What purpose does this serve? How is v=> true same as IEqualityComparer?

Upvotes: 0

Views: 1415

Answers (3)

Ivan Crojach Karačić
Ivan Crojach Karačić

Reputation: 1911

When your list has [1,2,3,4] and you convert it to a dictionary by list.ToDictionary(v=> v, v=>true); then your dictionary has this values 

[1,true]
[2,true]
[3,true]
[4,true].

The first value is the key the second is the value

EDIT:

just as @dkson said the second parameter is an elementSelector. You can see this in intellisense when you go to the 3rd of 4 entries :)

Upvotes: 1

sloth
sloth

Reputation: 101142

This is the method is used.

The second parameter (v => true) is the elementSelector (A transform function to produce a result element value from each element).

A list with the elements 1, 2 and 3 would result in a dictionary with the following mapping (all values are true):

1: true
2: true
3: true

Upvotes: 1

Ohad Schneider
Ohad Schneider

Reputation: 38142

You Take a look at the MSDN documentation. This is the overload taking a second IEqualityComparer argument:

ToDictionary<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>, IEqualityComparer<TKey>)

However, in your example you are using the overload which takes a Func<TSource, TElement> which is responsible for generating the values of the dictionary:

ToDictionary<TSource, TKey, TElement>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>)

(In your case, all values are simply true)

Upvotes: 1

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