Lambda Where Clause Error

Question

I'm trying to write a lambda like below but my syntax is incorrect.

Result = ListOfNumbers.Where(val => { val != Num1; val != Num2; }).ToList()[0];

The error I get is

Not all code paths return a value in lambda expression of type 'System.Func<int,int,bool>'

Perhaps there's a better way of doing this... I know there's the numbers 1, 2 and 3 (in that order) in ListOfNumbers. Num1 and Num2 at this point will both be either 1, 2 or 3 (they can't be the same though). I want my result to be the 'other' number from ListOfNumbers. Hope that's clear. If you can think of a neater way of doing it I'd love to hear it.

Any thoughts?

The title of your question has nothing to do with the actual question at all. Please edit the title so it refers to the question. — Botz3000
– Botz3000, Commented Jun 22, 2012 at 10:55
Thanks sorry hadn't updated the title from a previous question I was writing! — windowsgm
– windowsgm, Commented Jun 22, 2012 at 11:00

Andras Zoltan · Accepted Answer · 2012-06-22 10:59:47Z

2

you need to change it to

val => val != Num1 && val != Num2

If I write the code you've provided as it would be as a function you might see what's wrong:

public bool Predicate(int val)
{
   val != Num1;
   val != Num2;
}

I.e. - where's the return statement?

Although - note that that will actually fail to compile with the error Only assignment, call, increment, decrement, and new object expressions can be used as a statement - the compiler rules in lambdas are slightly different and so you get a different error but ultimately it's for the same kind of reason - in your case none of your lambda paths return anything.

edited Jun 22, 2012 at 10:59

answered Jun 22, 2012 at 10:52

Andras Zoltan

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Comments

Eren Ersönmez · Accepted Answer · 2012-06-22 10:52:45Z

1

Change the lambda as:

ListOfNumbers.Where(val =>  val != Num1 && val != Num2)

answered Jun 22, 2012 at 10:52

Eren Ersönmez

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Comments

Botz3000 · Accepted Answer · 2012-06-22 10:53:21Z

1

Did you actually want to do this?

Result = ListOfNumbers.Where(val => val != Num1 && val != Num2).ToList()[0];

Also, what if the list has no elements? You should better check that before accessing it by index.

answered Jun 22, 2012 at 10:53

Botz3000

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Habib · Accepted Answer · 2012-06-22 10:55:15Z

1

You are getting the error because inside Where clause you are not getting any bool, you need to change your lambda expression to :

Result = ListOfNumbers.Where(val =>  val != Num1 && val != Num2).ToList()[0];

answered Jun 22, 2012 at 10:55

Habib

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Comments

Akash KC · Accepted Answer · 2012-06-22 10:57:02Z

0

As your code expecting System.Func<int,int,bool> delegate which returns boolean value as in where condition So, you should define it in following way:

Result = ListOfNumbers.Where(val => { val != Num1 && val != Num2; }).ToList()[0];

answered Jun 22, 2012 at 10:57

Akash KC

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ZuTa · Accepted Answer · 2012-06-22 10:58:48Z

0

I think you want to produce something like this :

Result = ListOfNumbers.Where(val => val != Num1 && val != Num2).ToList()[0];

answered Jun 22, 2012 at 10:58

ZuTa

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bruno conde · Accepted Answer · 2012-06-22 11:00:39Z

0

If you create a block in your lambda empression you must use the return statement (if the lambda defines a result type).

If you just want the first element you can use FirstOrDefault instead of Where.

Result = ListOfNumbers.FirstOrDefault(val => val != Num1 && val != Num2 );

with a block:

Result = ListOfNumbers.FirstOrDefault(val => 
            { 
               var b = val != Num1 && val != Num2; 
               return b;
            } 
         );

I used && but I really don't know what is your condition...

answered Jun 22, 2012 at 11:00

bruno conde

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