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C# Querying With LINQ Query Operators Joins

Posted by Jon Andreas Grenness
Jon Andreas Grenness
5,055 Points

Struggeling to understand LINQ query to find birds

I can't wrap my head around how LINQ queries are meant to be formulated if I have to compare the results in to different lists even when re-watching video multiple times. Some help would be greatly appreciated.

Thank you in advance!

CodeChallenge.cs 
var myBirds = new List<Bird> 
{ 
    new Bird { Name = "Cardinal", Color = "Red", Sightings = 3 },
    new Bird { Name =  "Dove", Color = "White", Sightings = 2 },
    new Bird { Name =  "Robin", Color = "Red", Sightings = 5 }
};

var yourBirds = new List<Bird> 
{ 
    new Bird { Name =  "Dove", Color = "White", Sightings = 2 },
    new Bird { Name =  "Robin", Color = "Red", Sightings = 5 },
    new Bird { Name =  "Canary", Color = "Yellow", Sightings = 0 }
};

  var ourBirds = myBirds.Join(yourBird, b => b.Name, n => b.Name, (myBird, myBird.Name) => myBirds);

2 Answers

Steven Parker
Steven Parker
231,248 Points
Steven Parker
Steven Parker
231,248 Points

You're pretty close, you just need a little "fine tuning":

  • the first Join argument should be the name of the 2nd iterable "yourBirds" (plural, instead of "yourBird")
  • the inner key selector (third argument) should be n => n.Name (with "n" instead of "b")
  • the 2nd parameter of the result selector isn't used, but its name should not have a membership operator (".")

That 2nd lambda parameter can be anything, but I often like to use "_" (underscore) as the name of a parameter that won't be used. The name "unused" is also good.   :wink:

Jon Andreas Grenness
Jon Andreas Grenness
5,055 Points
Jon Andreas Grenness
Jon Andreas Grenness
5,055 Points

I changed the errors you pointed out, and renamed the (myBird, myBird.Name) => myBird to var ourBirds = myBirds.Join(yourBirds, b => b.Name, n => n.Name, (bird, name) => bird); and that worked.

Thanks!