Search between Two IEnumerable - LINQ

Question

Hi can you guys help me with this, I have try several things. I need to search between two IEnumerables, here is the code.

IEnumerable<Project> Projects = new[] { new Project {id = "1", lan = "test1"},  new Project {id = "2", lan = "test1"}}

IEnumerable<string> lan = new [] { "test1", "test2"};
IEnumerable<string> indexFiltered = ?;

I need to do a linq query that return the Project.id thats have any Project.lan in lan.

Any idea?

`I have try several things` Show us what have you tried. – Mahmoud Gamal Nov 07 '12 at 11:51 — Mahmoud Gamal, Nov 07 '12 at 11:51

score 3 · Answer 1 · answered Nov 07 '12 at 11:55

3

I'd use a HashSet rather than an array, as it allows check-if-contains as an O(1), rather than O(n), operation:

HashSet<string> lan = new HashSet<string> { "test1", "test2" };
IEnumerable<string> indexFiltered = projects
    .Where(p => lan.Contains(p.lan))
    .Select(p => p.id);

answered Nov 07 '12 at 11:55

Rawling

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+1 Learn't something I didn't know, will have a play about with `HashSet` myself in the future. – Adrian Thompson Phillips Nov 07 '12 at 12:00

Justin Harvey · Answer 2 · 2012-11-07T12:03:18.903

2

How about

indexFiltered = Projects.Where(p=>lan.Any(l=>l==p.lan)).Select(p=>p.Id);

edited Nov 07 '12 at 12:03

answered Nov 07 '12 at 11:53

Justin Harvey

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score 2 · Answer 3 · answered Nov 07 '12 at 11:54

2

 var results = projects.Where(p => lan.Contains(p.lan));

answered Nov 07 '12 at 11:54

Mahmoud Gamal

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score 0 · Accepted Answer · edited May 23 '17 at 12:04

0

Another efficient approach is using Enumerable.Join since it's implemented as a hash table:

IEnumerable<string> indexFiltered = from p in Projects
                                    join l in lan on p.lan equals l
                                    select p.id;

Why is LINQ JOIN so much faster than linking with WHERE?

The Join operator takes the rows from the first tables, then takes only the rows with a matching key from the second table, then only the rows with a matching key from the third table.

edited May 23 '17 at 12:04

Community

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answered Nov 07 '12 at 12:03

Tim Schmelter

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I will use the Join, is faster – Don Juan Nov 07 '12 at 12:28

score 0 · Answer 5 · answered Nov 07 '12 at 12:08

I would use IEnumerable.Join(). Internally it uses the HashSet to do the distinction:

var Projects = new[] { new {id = "1", lan = "test1"},  new {id = "2", lan = "test1"}};
var lan = new [] { "test1", "test2"};

var results = Projects.Join(lan,
                              project => project.lan,
                              lanName => lanName,
                              (project, lanName) => project.id);

foreach (var result in results)
{
    Console.WriteLine("ID found: ", result);
}

Search between Two IEnumerable - LINQ

5 Answers5