not getting any result from the list

Question

2.50/5 (2 votes)

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Hello All,

I have list with few items such as "codeproject", "stackoverflow", "msdn". I filter the list using Where and assign to a variable as below,

C#

var output= list.Where(i=>i.Length>5);

but there is nothing in the output.

I cannt figured out, please help me.

Posted 24-May-12 4:06am

Hai Qui

Updated 24-May-12 9:11am

Wendelius

v2

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Comments

Sergey Alexandrovich Kryukov 24-May-12 11:39am

Why? Did you look properly? Run under debugger?
--SA

7 solutions

Solution 2

I'm sure it's there; you only failed to see it by some reason. This will show some output:

C#

string[]
using System.Linq;

//...

list = new string[] {
    "CodeProject", "StackOverflow", "MSDN", "Google", "Bing", "Yahoo", };
var output = list.Where(i => i.Length > 5);
foreach (var item in output)
    System.Console.WriteLine(item);

As expected, on output you will see:

CodeProject
StackOverflow
Google

You can see the same if you make list a list of the type System.Collection.Generic.List<string>. What to try? :-)

—SA

Posted 24-May-12 5:38am

Sergey Alexandrovich Kryukov

Updated 24-May-12 5:40am

v3

Comments

Maciej Los 24-May-12 12:17pm

My 5!

Sergey Alexandrovich Kryukov 24-May-12 12:19pm

Thank you, Maciej.
--SA

Pete O'Hanlon 25-May-12 4:08am

The reason he hasn't seen it is that the query hasn't been evaluated. Iterating over the query actually executes it (as does operations like ToList or Skip). This is known as deferred execution, and it can have unfortunate side effects if you aren't aware of it.

Sergey Alexandrovich Kryukov 28-May-12 17:49pm

Good point, thank you.
--SA

Solution 6

because of Deferred Execution[^] and Where and Select[^]

Hope it helps :)

Posted 24-May-12 11:22am

Mohammad A Rahman

Comments

Pete O'Hanlon 25-May-12 4:05am

My 5. Most people seem to have missed that the query hasn't actually been executed.

Mohammad A Rahman 25-May-12 4:41am

Thank you.

Solution 1

What kind of "list" are you using?
I've tried with a List<string> and it works fine

C#

List<string> list = new List<string>();
list.Add("codeproject");
list.Add("stackoverflow");
list.Add("msdn");

var output = list.Where(i => i.Length > 5);

If I execute this code, the ouptput.Count() is 2

Posted 24-May-12 5:33am

Chabi Blazquez

Updated 24-May-12 9:12am

v2

Solution 3

This works perfectly fine for me as expected:

C#

string[] list = {"codeproject","stackoverflow", "msdn" };
var output = list.Where(i => i.Length > 5);
// results 2 strings - codeproject & stackoverflow

Posted 24-May-12 5:59am

Sandeep Mewara

Solution 5

List<string> lste = new List<string>();
lste.Add("codeproject");
lste.Add("stackoverflow");
lste.Add("msdn");

var output = lste.FindAll( i => i.Length > 5);

Posted 24-May-12 7:52am

Sanjit.Prasad

Updated 24-May-12 7:55am

v2

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Pete O'Hanlon · Accepted Answer · 2012-05-24T06:24:00

Solution 4

There is nothing in the output at this stage because you haven't actually evaluated the expression. All you've done is create a query expression. You don't get any output from it until you attempt to do something like a First or Take or Count, etc...

Posted 24-May-12 6:24am

Pete O'Hanlon

Comments

Mohammad A Rahman 24-May-12 17:23pm

Exactly as it is the Deferred Execution :)

Clifford Nelson · Accepted Answer · 2012-05-24T12:12:00

Solution 7

The easy solution for you is to convert the Linq result into a list:

var output= list.Where(i=>i.Length>5).ToList();

you can also convert it to an Array with the same result.

What happens is converting it to a List or Array forces immediate execution.

Posted 24-May-12 12:12pm

Clifford Nelson

Updated 24-May-12 12:13pm

v2