LINQ custom sort using comparer

Question

I have a class:

public class Item
{
  public int ownerID;
  public decimal value;
}

And an array of objects

Item[] items;

That looks like:

ownerID     value
476478      0.65
636566      0.2

And I have a second class

public class Owner
{
  public int ownerID;
  public int index;
}

And an array of objects

Owner[] owners;

The "owners" is sorted in specific order according the index and looks like:

ownerID    index
636566     1
476478     2

How can I sort the "items" in the same order as the "owners" using LINQ and comparer?

Would expect something like:

items = items.OrderBy(o => o.OwnerID, comparer(o))

where comparing made by "index".

Thanks a lot.

If anything, `items.OrderBy(i => i.OwnerID...)` even single letter names should be chosen wisely. — Zohar Peled, Sep 11 '17 at 13:13
Can you change the `Item` class to hold a reference to `Owner` instead of just it's id? — Zohar Peled, Sep 11 '17 at 13:16
Can there be items that have no owners, or owners that have no items? — Zohar Peled, Sep 11 '17 at 13:18
That is not what you tried. This is what you want. I mean TRIED, wrote a comparer or anything what should lead to expected result. Your question is vague. Please add an example how data looks like and what is expected result. Now this comparer should compare index to what? Can't you just join 2 tables and sort by multiple fields? — Renatas M., Sep 11 '17 at 13:19

score 2 · Accepted Answer · answered Sep 11 '17 at 13:19

2

Assuming what you're trying to do is to order the items using the index property from the Owner object, something like this should do the job:

var joined = items.Join(owners, item => i.OwnerId, owner => o.OwnerId, (item, owner) => new
{
    Item = item,
    Index = owner.Index
});

var orderedItems = joined.OrderBy(j => j.Index).Select(j => j.Item);

answered Sep 11 '17 at 13:19

Rodrigo Vedovato

1,008
6
11

Excelent! Thanks. – Ilan Sep 12 '17 at 06:49
But I have another problem - the ordering of "items" should be not according the "index" of "owners" but according actual location of ownerID in the array. How can I change your code? Thanks in advance. – Ilan Sep 12 '17 at 06:51
Ok found the way to do this. – Ilan Sep 12 '17 at 07:48

score 0 · Answer 2 · answered Sep 11 '17 at 13:13

0

Try this

//Initiate new object 
    Item items= new Items(); 
//Sort the items based on owner ID 
List myList = items.OrderBy(x => x.ownerID).ToList();

answered Sep 11 '17 at 13:13

score 0 · Answer 3 · answered Sep 11 '17 at 13:13

You can turn your Owner array into a Dictionary<int, int> like this:

Dictionary<int, int> ownerDict = owners.ToDictionary(x => x.ownerID, y => y.index);

And then use that to order the items like:

Item[] orderedItems = items.OrderBy(i => ownerDict[i.ownerID]).ToArray();

To order the items by the same index, the owners are ordered.

score 0 · Answer 4 · answered Sep 11 '17 at 13:14

You can use LINQ .Select(), it will use a collection iterator to process the collection in its natural order. The lambda inside the Select can then be used to fetch each corresponding item from items. Like this:

var itemsInOrder = owners
    .Select(x => items.First(item => item.ownerId == x.ownerId))
    .ToArray();

This assumes that every ownerId can be found in items. If that is not true then you will have to extend it a little, e.g. like this:

var itemsInOrder = owners
    .Select(x => items.FirstOrDefault(item => item.ownerId == x.ownerId))
    .Where(item => item != null)
    .ToArray();

LINQ custom sort using comparer

4 Answers4