Searching if value exists in a list of objects using Linq

Question

Say I have a class Customer which has a property FirstName. Then I have a List<Customer>.

Can LINQ be used to find if the list has a customer with Firstname = 'John' in a single statement.. how?

Andriy Volkov · Accepted Answer · 2012-11-25 18:22:51Z

578

LINQ defines an extension method that is perfect for solving this exact problem:

using System.Linq;
...
    bool has = list.Any(cus => cus.FirstName == "John");

make sure you reference System.Core.dll, that's where LINQ lives.

edited Nov 25, 2012 at 18:22

answered Jul 1, 2009 at 19:59

Andriy Volkov

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5 Comments

RichardOD Over a year ago

Any is good, I wonder how many developers use Count when they should use Any?

jmservera Over a year ago

You can also do a case insensitive search: cus => cus.FirstName.Equals("John", StringComparison.CurrentCultureIgnoreCase)

Blackunknown Over a year ago

I know this is an old question but why aren't we making use of the Exists method? Seeing as it is made to see if things exist.

Andriy Volkov Over a year ago

Because not all collections have Exists, and it does not take a lambda expression, but rather the object we are looking for itself.

Gullu Over a year ago

@zvolkov, Any ideas why my resharper is suggesting I use bool has = list.All(cus => cus.FirstName != "John"); Is this more optimal ?

Jon Skeet · Accepted Answer · 2009-07-01 20:01:50Z

126

zvolkov's answer is the perfect one to find out if there is such a customer. If you need to use the customer afterwards, you can do:

Customer customer = list.FirstOrDefault(cus => cus.FirstName == "John");
if (customer != null)
{
    // Use customer
}

I know this isn't what you were asking, but I thought I'd pre-empt a follow-on question :) (Of course, this only finds the first such customer... to find all of them, just use a normal where clause.)

answered Jul 1, 2009 at 20:01

Jon Skeet

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4 Comments

mqp Over a year ago

I'd point out that you might appreciate having done this later when it comes to debugging, if you find yourself suddenly curious which customer it was that fit the criteria.

barneymc Over a year ago

Just bumping this answer up one cos I love the way SO community goes the extra step to add even more to the question/answer.

Shaiju T Over a year ago

thanks it helped me, but sometimes i just want to get bool result , so in that case .Any or .FindIndex is used here which is fast ?

Jon Skeet Over a year ago

@stom: They're both O(N), basically... they're just linear searches.

Unu · Accepted Answer · 2016-08-09 22:48:20Z

30

One option for the follow on question (how to find a customer who might have any number of first names):

List<string> names = new List<string>{ "John", "Max", "Pete" };
bool has = customers.Any(cus => names.Contains(cus.FirstName));

or to retrieve the customer from csv of similar list

string input = "John,Max,Pete";
List<string> names = input.Split(',').ToList();
customer = customers.FirstOrDefault(cus => names.Contains(cus.FirstName));

edited Aug 9, 2016 at 22:48

Unu

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answered Jul 13, 2009 at 18:18

Mike Sackton

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Comments

jmservera · Accepted Answer · 2009-07-01 20:28:57Z

10

Using Linq you have many possibilities, here one without using lambdas:

//assuming list is a List<Customer> or something queryable...
var hasJohn = (from customer in list
         where customer.FirstName == "John"
         select customer).Any();

answered Jul 1, 2009 at 20:28

jmservera

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Comments

Carlos Landeras · Accepted Answer · 2013-06-17 07:02:10Z

7

customerList.Any(x=>x.Firstname == "John")

edited Jun 17, 2013 at 7:02

Carlos Landeras

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answered Jul 1, 2009 at 20:01

Chris Brandsma

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4 Comments

jason Over a year ago

This does not answer the question "if" such an entry exists; it merely enumerates the values if they do exist. An extra step is needed to determine if this enumeration is nonempty.

Chris Brandsma Over a year ago

Then change the Where to Any. Probably more philosophical for me. I rarely need to know if without caring which ones they are. @jmservera: you were right. I gave up LINQ a while back and now use Lambda exclusively.

Judah Gabriel Himango Over a year ago

I don't mean to be pedantic when I say that using the lambda calls is still technically using LINQ. (In particular, you're using LINQ-to-Objects.) You're just using the method calls rather than language keywords.

dotnetN00b Over a year ago

How does this answer differ from the zvolkov's?

Ian Boyd · Accepted Answer · 2012-12-05 22:44:27Z

4

The technique i used before discovering .Any():

var hasJohn = (from customer in list
      where customer.FirstName == "John"
      select customer).FirstOrDefault() != null;

answered Dec 5, 2012 at 22:44

Ian Boyd

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Comments

M4N · Accepted Answer · 2009-07-01 20:01:46Z

3

List<Customer> list = ...;
Customer john = list.SingleOrDefault(customer => customer.Firstname == "John");

john will be null if no customer exists with a first name of "John".

answered Jul 1, 2009 at 20:01

M4N

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3 Comments

Jon Skeet Over a year ago

That will throw an exception if more than one customer is called John.

M4N Over a year ago

Thanks for the comment. I'll leave the answer as a partially correct example.

RichardOD Over a year ago

It's still valid in a scenario when you are sure there is 1 and you want an exception to be raised if more than one, so I think it is good that you didn't delete it.

Fabio Stratotti · Accepted Answer · 2017-06-13 16:42:43Z

3

Try this, I hope it helps you.

 if (lstCustumers.Any(cus => cus.Firstname == "John"))
 {
     //TODO CODE
 }

answered Jun 13, 2017 at 16:42

Fabio Stratotti

551 bronze badge

1 Comment

Tony_Henrich Over a year ago

That's the same as the accepted answer from over 8 years ago. Please make sure your answer is unique among all the answers.

Krassi · Accepted Answer · 2009-07-01 20:14:21Z

1

Another possibility

if (list.Count(customer => customer.Firstname == "John") > 0) {
 //bla
}

answered Jul 1, 2009 at 20:14

Krassi

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1 Comment

RichardOD Over a year ago

Its' preferable to use Any in this scenario.

KRM · Accepted Answer · 2023-06-21 15:39:31Z

0

Include using System.Linq

Use Trim() if there should be a match even with leading and trailing whitespaces.

Use StringComparison.CurrentCultureIgnoreCase if the match needs to
be case insensitive.

using System.Linq;
...
    bool has = list.Any(cus => cus.FirstName.Trim().Equals("John", StringComparison.CurrentCultureIgnoreCase));

answered Jun 21, 2023 at 15:39

KRM

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