Lambda Expression with foreach loop in C#

Question

 var coupon=" ";

 foreach(var p in products)
 {
     var query = products.Where(b => b.getId() == p.getId()).ToList();

     if (query != null)
     {
         foreach(var q in query)
         {
             coupon = q.getName();
             Console.WriteLine(coupon);
         }
     }
 }

Can anyone tell me what will be the lambda expression of this code-chunk

Your question is completely unclear. For which part of this code you need an expression? Anyway this question is far too broad, in particlar as you didn´t provide *any* own affords. We´re not here to do your job. — MakePeaceGreatAgain, Sep 05 '18 at 19:27

score 4 · Accepted Answer · answered Sep 05 '18 at 19:03

Not every loop operation is a natural fit for a lambda expresssion. Lambda expressions are useful for projections of data - i.e. transforming it from one form to another - applying formulae etc, but: that isn't what you're doing here. You're doing something with the data (the Console.WriteLine. You could do something with LINQ here involving SelectMany, but... it would become less readable, not more.

What you have alread is just fine. The only changes I'd make are:

to remove the if (query != null) test - that is never going to be false
remove the ToList() - there's no need to create a new list just to iterate it
no need to declare coupon before it is needed
I might hoist the p.getId()

So:

 foreach(var p in products)
 {
     var id = p.getID();
     foreach(var q in products.Where(b => b.getId() == id))
     {
         var coupon = q.getName();
         Console.WriteLine(coupon);
     }
 }

For each product `p`, it writes out the coupon name of all products `q` that share the ID with `p` (including `p` itself). I wonder what ID that is. I agree with your statement _Not every loop operation is a natural fit for a lambda expresssion._ However, if we wanted to create an `IEnumerable<>` of all those coupon names, instead of `Console.WriteLine`, then it might fall under the category of projections of data... — Jeppe Stig Nielsen, Sep 05 '18 at 20:47

John Cummings · Answer 2 · 2018-09-05T21:18:44.117

0

There is a lambda expression in your code block and it is the only argument to Where and is as follows:

b => b.getId() == p.getId()

In this particular case, the lambda is effectively (though not technically) a Predicate, which is a fancy name for a function that tests if something is true or false

edited Sep 05 '18 at 21:18

answered Sep 05 '18 at 18:44

John Cummings

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Technically, the argument required by `.Select` is a `Func`, not a `Predicate` like in .NET-2.0-style methods such as `List<>.FindAll(…)`, however `Func` and `Predicate` are equivalent (same signature and return type). – Jeppe Stig Nielsen Sep 05 '18 at 20:53
Good point, I have updated my answer with that clarification. – John Cummings Sep 05 '18 at 21:20

Lambda Expression with foreach loop in C#

2 Answers2