CODEWITHSUNDEEP
c#linq
Hem
Hem

Reputation: 729

How to understand this lambda expression?

I'm a C# novice. Can someone help me understanding this C# lambda expression?

var projs = allCustomers.SelectMany(osd => osd.phoneNumbers,
                                   (osd, osv) => new { customer= osd, phoneNumber= osv });

Thanks/Hem

Upvotes: 0

Views: 110

Answers (1)

Selman Genç
Selman Genç

Reputation: 101680

You are using this overload of SelectMany.

public static IEnumerable<TResult> SelectMany<TSource, TCollection, TResult>(
      this IEnumerable<TSource> source,
      Func<TSource, IEnumerable<TCollection>> collectionSelector,
      Func<TSource, TCollection, TResult> resultSelector
)

There are three parameters:

source :
Type: System.Collections.Generic.IEnumerable<TSource>
A sequence of values to project.

collectionSelector
Type: System.Func<TSource, IEnumerable<TCollection>>
A transform function to apply to each element of the input sequence.

resultSelector
Type: System.Func<TSource, TCollection, TResult>
A transform function to apply to each element of the intermediate sequence.

In your case, source is the allCustomers, collectionSelector is the expression: 

osd => osd.phoneNumber

and the resultSelector is: 

(osd, osv) => new { customer= osd, phoneNumber= osv }

Here the first expression says take each customer and return it's phoneNumbers.In the second expression, the type of osd is customer, osv is phoneNumber and the result is an anonymous type.It takes each customer and the phone number and creates an anonymous type using these values.

Here is an example of what this query does:

Customer - Phone Numbers
------------------------
John      1234567,2331212,1122334
Jack      1456771,9485323
Juliet    2401232

The result would be:

John   1234567
John   2331212
John   1122334
Jack   1456771
Jack   9485323
Juliet 2401232

Upvotes: 9

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