CODEWITHSUNDEEP
c#listsorting
VincentH
VincentH

Reputation: 383

Reorder list by a property I don't have

I have a bog-standard list in C#: List (where Channel is a TV channel). Channel is defined as:

public class Channel
{
    public int ChannelId { get; set; }
    public string ChannelName { get; set; }
}

My ORM populates a list of Channels, which comes from the database in Channel Id order. I need to re-order the list based on a new custom sort property, say ChannelOrder, but I can't modify the underlying database.

Any thoughts on how to do this, without modifying the underlying DB?

So for instance, if I current have coming from the db:

ChannelId =1, ChannelName = "BBC1", ChannelId =2, ChannelName = "BBC2", ChannelId =3, ChannelName = "ITV"

I might want them ordered as BBC2, BBC1, ITV, basically a custom order.

Upvotes: 0

Views: 141

Answers (2)

It'sNotALie.
It'sNotALie.

Reputation: 22794

You could maybe use another class that returns an "attached" property, kind of like attached properties in WPF:

public static class ChannelSort
{
    static Dictionary<Channel, int> _dict = new Dictionary<Channel, int>();
    public static int GetSort(this Channel c)
    {
        return _dict[c] //will throw if key's not found,
        //may want to handle it for more descriptive exception
    }
    public static int SetSort(this Channel c, int sort)
    {
        _dict[c] = sort;
    }
}

And then you could do this:

var result = unsortedList.OrderBy(c => c.GetSort());

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1499840

If you're happy to do this in-process (rather than as part of the query) you can use:

var orderedChannelNames = new[] { "BBC2", "BBC1", "ITV", ... };
var sorted = unsorted.OrderBy(ch => orderedChannelNames.IndexOf(ch.ChannelName));

Alternatively, if you know all the channels in your list will be present:

var map = unsorted.ToDictionary(ch => ch.ChannelName);
var sorted = orderedChannelNames.Select(name => map[name]);

Upvotes: 2

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