C# LINQ - Find object in list between two properties

Question

I haven't worked with LINQ before, but I know how efficient it is.
I have created a List with an object which you can see below:

public sealed class Item
{
    public long Start { private set; get; }
    public long End { private set; get; }
    public Item(string start, string end)
    {
        this.Start = Convert.ToInt64(start);
        this.End = Convert.ToInt64(end);
    }
}

This will be populated with DataSets containing round about 200k Items.
Now, I want to select the best single item between the properties 'Start' and 'End'.

this.ItemList.Add(new Item(100000, 100002));
this.ItemList.Add(new Item(100003, 100006));
this.ItemList.Add(new Item(100007, 100012));
this.ItemList.Add(new Item(100013, 100026));
this.ItemList.Add(new Item(100027, 100065));

From another tool, I've got the value: 100009

How can I get the object new Item(100007, 100012) back with LINQ? Does anyone have any suggestions?

What if given value fits two items as difference to both is equal? In particular what happens when the provided value is exactly between the end of one and the start of the next interval? — MakePeaceGreatAgain, Feb 16 '16 at 13:56
It's not clear what your criteria is - do you want to find all objects where start and end are both between two arbitrary values? — D Stanley, Feb 16 '16 at 13:57

score 4 · Answer 1 · edited May 23 '17 at 11:45

4

Sounds like a simple Where query should suffice:

long value = 100009;
var found = ItemList.Where(item => item.Start <= value && item.End >= value);

This will yield an IEnumerable<Item> containing all matching items. You can use .First()/.FirstOrDefault() to get the first matching item or continue to filter the result until you get the one you want.

Note that, if you really have 200k entries, a List might not be the most efficient data structure to search in (you have O(n) complexity). If performance is an issue, you might want to consider using a SortedList and a binary search algorithm instead.

edited May 23 '17 at 11:45

Community

1
1

answered Feb 16 '16 at 13:59

Heinzi

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seems `First` rather: _i want to select the best one_ – Grundy Feb 16 '16 at 14:00
2

@Grundy: That depends on his definition of "best": first? smallest interval? closest to one of the boundaries? – Heinzi Feb 16 '16 at 14:01
yep, but _one_ i think say about select just one – Grundy Feb 16 '16 at 14:01
1

@Grundy: I've modified my answer and mentioned `First` as an option. – Heinzi Feb 16 '16 at 14:03
I'd use FirstOrDefault instead, because it avoids null reference exception – MVCDS Feb 16 '16 at 14:03
1

@MVCDS Actually it avoids InvalidOperationException. – juharr Feb 16 '16 at 14:05
2

@MVCDS: It's the other way around: First will throw an `InvalidOperationException`, FirstOrDefault will yield null (which might later lead to a null reference exception, if you're not careful). – Heinzi Feb 16 '16 at 14:06

C# LINQ - Find object in list between two properties

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