LINQ : Checking against each other item in a list

Question

I have class like below

public class Item { public long Id {get;set;} public long GroupingId {get;set;} public long Weight {get;set;} public long Tolerance {get;set;} }

Now I have list of Items with different grouping id. Lets say

List<Item> items = GetItems();

Now I need to group based groupings id, and make check for each item in that group against each other. How would I do that in LINQ efficiently. Any help much appreciated.

IDictionary<long, long[]> matches = new Dictionary<long, long[]>(); foreach(groupedItems in items.GroupBy(p=>p.GroupingId)) { foreach(item in groupItems) { // Check item with other items in group items // and if condition is correct take those 2 items. // lets say the condition is // (item.Weighting - other.Weighting) > item.Tolerance // duplicates could be removed // lets condition for 1,2 is done means no need to do 2 against 1 var currentItem = item; var matchedOnes = groupItems.Where(p => (Math.Abs(p.Weighting - currentItem.Weighting) > currentItem .Tolerance) && p.Id != currentItem.Id) .ToList(); if (!matchedOnes.Any()) continue; matches.Add(currentItem.Id, matchedOnes .Select(p=>p.Id).ToArray()); } }

I did like above, but its giving duplicates(1,2 and 2,1 are duplicates).. How would I remove the duplicate checks

What exactly checks do you want to do? It seems that you want to throw all items with difference more than tolerance, but in this case you should compare value with average value, but you compare with other values in group. In this case, if you have any pair of items with difference more than tolerance you will throw away whole group. — Kirill Bestemyanov
– Kirill Bestemyanov, Commented May 28, 2013 at 11:20
I need to check the difference in weighting of two items in the group with greater than the item 1 tolerance. Math.Abs(item1.weighting-item2.weighting) > item1.Tolerance — Bhaskar
– Bhaskar, Commented May 28, 2013 at 11:24
first make distinct list of GroupingId Like List<long> lst = items.Select(h => h.GroupingId).Distinct().ToList(); — Kamran Shahid
– Kamran Shahid, Commented May 28, 2013 at 11:32
@FrancescoDeLisi I have updated it. There is no field called answer — Bhaskar
– Bhaskar, Commented May 28, 2013 at 14:10

Rawling · Accepted Answer · 2013-05-28 12:16:56Z

3

As a simple change, try exchanging p.Id != answer.Id for p.Id > answer.Id in your groupItems.Where(...) line.

answered May 28, 2013 at 12:16

Rawling

50.3k7 gold badges94 silver badges131 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Francesco De Lisi Over a year ago

Excellent, if answer means what you think and belongs to groupItems.

Serge · Accepted Answer · 2013-05-28 11:40:23Z

Do you mean this:

 var items = new List<Tuple<int, int>>() { new Tuple<int, int>(1, 1) , new Tuple<int, int>(1, 2) , new Tuple<int, int>(2, 2) , new Tuple<int, int>(2, 2) , new Tuple<int, int>(2, 3) , new Tuple<int, int>(3, 2) , new Tuple<int, int>(3, 3) , new Tuple<int, int>(4, 4) , new Tuple<int, int>(4, 3) , new Tuple<int, int>(4, 4) }.Select(kp => new { id = kp.Item1, data = kp.Item2 }); var res = ( from i1 in items from i2 in items where i1.id < i2.id /* Custom Filter goes there */ && i1.data == i2.data select new { i1 = i1, i2 = i2 } );

Check out Tuple.Create which can save you a couple of characters since you need not specify the generic types: msdn.microsoft.com/en-us/library/dd387181.aspx

vc 74 · Accepted Answer · 2013-05-28 14:10:37Z

Try this

var pairs = Enumerable.Range(0, items.Count()).SelectMany(index => items.Skip(index + 1).Select(right => new { left = items.elementAt(index), right })); var matches = pairs.Where(item => (item.left.Weight - item.right.Weight) > item.left.Tolerance);

The first part creates all the pairs that have to be compared like (1, 2), (1, 3), (2, 3) for a collection of 3 items. The second part selects the pairs that match your condition.

I've also removed the grouping code which you already figured out (items = groupItems).

Is it me, or is this a scenario where LINQ causes completely unreadable code?

Collectives™ on Stack Overflow

LINQ : Checking against each other item in a list

3 Answers 3

1 Comment

1 Comment

1 Comment

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

1 Comment

Related