Sort objects in List by properties on the object

Question

I have a List of objects in C#. All the objects contain properties code1 and code2 (among other properties). The list of objects is in no particular order. I need to sort the list of objects by their code1 and code2 properties.

Example:

List -> object = id, name, code1, code2, hours, amount.

Example code 1 = 004
Example code 2 = 001, 002, 003, 004, 016
Example code 1 = 005
Example code 2 = 001, 002, 003, 004

So after the sort I would want the objects in the following order

+1 Not sure why you were downvoted.

Adam Houldsworth
– Adam Houldsworth

2012-04-04 14:34:51 +00:00
Commented Apr 4, 2012 at 14:34 — Adam Houldsworth
– Adam Houldsworth, Commented Apr 4, 2012 at 14:34

Adam Houldsworth · Accepted Answer · 2012-04-04 15:09:58Z

27

You could use linq extensions (leaving the original list unsorted):

var sorted = theList.OrderBy(o => o.code1).ThenBy(o => o.code2);

To replace the original list with a sorted one, make a slight amendment (not very efficient, it creates a new list):

theList = theList.OrderBy(o => o.code1).ThenBy(o => o.code2).ToList();

This assumes that your list is of the correct type, something like:

List<MyClass> theList = new List<MyClass>();

And not a list of objects, in which case you would need to make use of .Cast<>() or .OfType<>().

edited Apr 4, 2012 at 15:09

answered Apr 4, 2012 at 14:29

Adam Houldsworth

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3 Comments

George Duckett Over a year ago

Note that this leaves the original list unsorted.

phoog Over a year ago

The ToList call, as I imagine you are aware, still does not sort the original list; it creates a new list with the items in order. That will most likely be slightly slower than sorting the list in place; it will certainly require more memory, and if the list is large, the extra memory pressure may have a significant impact on performace.

Adam Houldsworth Over a year ago

@phoog Fair enough - I held off providing an implementation of the Sort method as I couldn't be confident of it without compiling and trying it. I've amended my answer to be a little more explicit.

phoog · Accepted Answer · 2012-04-04 15:06:48Z

11

Note that Adam Houldsworth's answer with the .ToList() call needlessly creates a new list. If your list is large, this may create unacceptable memory pressure. It would most likely be better to sort the list in place by providing a custom comparison function:

theList.Sort((a, b) =>
    {
        var firstCompare = a.code1.CompareTo(b.code1);
        return firstCompare != 0 ? firstCompare : a.code2.CompareTo(b.code2);
    });

Alternatively, if this ordering is an intrinsic property of your type, you could implement IComparable<T> on your type, and just call

theList.Sort();

... which will use the IComparable<T>.CompareTo() implementation.

answered Apr 4, 2012 at 15:06

phoog

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1 Comment

phoog Over a year ago

@AdamHouldsworth And of course your approach gives neater code. I'd probably use Linq if I were certain that the list would never contain more than a handful of items, since performance would not likely be an issue in that case.

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