C# foreach to linq

Question

I was wondering if there wasn't an optimal way for this code.

List<CollectionFormFieldRecord> dataFields = new List<CollectionFormFieldRecord>();
foreach (CollectionRelationModel relation in relations)
{
     foreach (var field in visibleFields)
     {
          if (field.SourceCollectionsID == relation.ChildCollectionID)
            dataFields.Add(field);
     }
}

When a field (visibleFields) has a SourceCollectionsID that exists in the relations list then the field must be added to a separated list.

I tried somethings with LINQ but didn't know how to compare a property with a property in a list.

possible duplicate of [Compare Two Lists Via One Property Using LINQ](http://stackoverflow.com/questions/17323804/compare-two-lists-via-one-property-using-linq) — user1666620, Aug 31 '15 at 10:50

score 2 · Answer 1 · answered Aug 31 '15 at 10:51

2

You can do this using linq

dataFields = (from relation in relations 
                    from field in visibleFields 
                    where field.SourceCollectionsID == relation.ChildCollectionID 
                    select field).Select(field => field).ToList();

but I do prefer using foreaches instead

answered Aug 31 '15 at 10:51

Kamil Budziewski

22,699
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Why do you prefer foreaches? I thought linq could be more performant? – PJDW Aug 31 '15 at 11:50
1

@PJDW no it isn't http://codereview.stackexchange.com/questions/14197/is-the-linq-version-faster-than-the-foreach-one – Kamil Budziewski Aug 31 '15 at 11:51

score 2 · Answer 2 · edited May 23 '17 at 10:26

2

The code you showed us has complexity of O(N square). Try to use .Join method, so you will have complexity close to O(N) due to hashing. The code you should use is

dataFields = visibleFields.Join(relations, vF => vF.SourceCollectionsID, r => r.ChildCollectionID, (visibleField, relation) => visibleField).ToList();

For better understand about complexity look at my answer for this question

edited May 23 '17 at 10:26

Community

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answered Aug 31 '15 at 11:06

David Gregor

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score -1 · Accepted Answer · answered Aug 31 '15 at 10:51

-1

I can be similar to this

var dataFields = dataFields .Where(f => relations.Any(r => f.SourceCollectionsID ==r.ChildCollectionID))
                .ToList()

answered Aug 31 '15 at 10:51

I4V

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C# foreach to linq

3 Answers3