LINQ Order By to select lowest Index

Question

I am relatively new to LINQ and don't know how to do an Order By. I have an IEnumerable list of myObject and want to do something like select first myObject from myObjectList order by myObject.id asc How can I accomplish this? Thanks

Could you clarify this please? Do you *actually* need the ordered results, or just the result with the lowest ID? Do you need the *index* of that entry, or just the ID? — Jon Skeet, Sep 30 '10 at 19:10
If you only need the result with the lowest ID, there is an implementation of a MinBy extension method [here](http://stackoverflow.com/questions/914109/how-to-use-linq-to-select-object-with-minimum-or-maximum-property-value). It was written by some fella' I've never heard of though (his name is Jon Skeet, or something like that), so I dunno how much I trust it. — Chris Shouts, Sep 30 '10 at 20:22
@Jon...some clarity. I need the object in the list that has the lowest Id. — MikeTWebb, Oct 01 '10 at 19:20

score 7 · Accepted Answer · answered Sep 30 '10 at 19:10

Ascending is the default order by direction.

var query = from myObject in myObjectList
            orderby myObject.id
            select myObject;

Object o = query.FirstOrDefault();

If you want descending, you will want to use orderby myObject.id descending.

score 3 · Answer 2 · answered Sep 30 '10 at 19:10

3

var obj = myObjects.OrderBy(o => o.id).First();

answered Sep 30 '10 at 19:10

danijels

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Branimir · Answer 3 · 2010-09-30T19:20:50.047

2

Use the First method.

For example:

var data = (from o in Orders
           order by o.OrderID
           select o.Name).First();

edited Sep 30 '10 at 19:20

answered Sep 30 '10 at 19:11

Branimir

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score 1 · Answer 4 · answered Sep 30 '10 at 20:09

If you want the item with the lowest ID, you don't need an OrderBy... It is much faster to just enumerate the list once, since this operation has O(n) complexity whereas a typical sort has O(n log n) complexity. You can do it with a foreach loop, or use an extension method like this one:

    public static T WithMin<T, TValue>(this IEnumerable<T> source, Func<T, TValue> selector)
    {
        var min = default(TValue);
        var withMin = default(T);
        bool first = true;
        foreach (var item in source)
        {
            var value = selector(item);
            int compare = Comparer<TValue>.Default.Compare(value, min);

            if (compare < 0 || first)
            {
                min = value;
                withMin = item;
            }
            first = false;
        }
        return withMin;
    }

Use it like that:

var objectWithMinId = myObjectList.WithMin(o => o.Id);

what if the backing store (e.g. SQL) has an index and LINQ can take advantage of that? enumerating the full set is akin to a full table scan. — magma, Jul 08 '15 at 00:50
@magma, yes, but in this case it was pretty clear that the backing store was an in-memory collection, so I wrote my answer with that in mind. If the backing store is a database, you're better off doing an OrderBy and take the first item. — Thomas Levesque, Jul 08 '15 at 08:07

score 0 · Answer 5 · answered Aug 30 '14 at 07:37

0

I would prefer using FirstOrDefault() in place of First() , in case your query does not return any elements then First() will throw a Exception.

var myObj = (from myObject in myObjectList orderby myObject.id select myObject).FirstOrDefault();

answered Aug 30 '14 at 07:37

Rohit Jindal

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score 0 · Answer 6 · answered Sep 30 '10 at 19:11

Ascending is the default if you wanted the reverse just use OrderByDescending()

var obj = myObjectList.OrderBy(x => x.id).First();

if you needed the ID or some other property from the object you can keep the same line

int myID = myObjectList.OrderBy(x => x.id).First().id;

score 0 · Answer 7 · answered Sep 30 '10 at 20:09

0

Your query should look like following:

var yourquery = (from myObject in myObjectList
                 orderby myObject.id
                 select myObject).First();

Now the variable yourquery contains the object you require.

answered Sep 30 '10 at 20:09

explorer

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LINQ Order By to select lowest Index

7 Answers7