CODEWITHSUNDEEP
c#linqsorting
user3781214
user3781214

Reputation: 357

Linq Custom Sorting

I have a list of objects containing 2 properties (id and letter). There can be exactly 4 different letter values for these objects (a, b, c and d). When I sort these objects, first I want to sort by letter. Then I would like to sort by id. When I sort by letter, I want the order to be a, b, d, c. I'm having trouble getting this custom sorting. When using linq, I tried something like this: 

ListOfObjects.OrderBy(t => t.letter).ThenBy(t => t.letter.StartsWith("c") ? 2 : 1).ThenBy(t => t.id);

My thinking behind this was that you could simply move the objects where the letter starts with c down to the bottom of the list. However, this doesn't seem to work. Do you guys have any ideas? Any help would be greatly appreciated.

Upvotes: 2

Views: 1180

Answers (2)

poke
poke

Reputation: 388253

You can create a mapping that translates the letters into a total order:

Dictionary<char, int> mapping = new Dictionary<char, int>()
{
    { 'a', 1 },
    { 'b', 2 },
    { 'd', 3 },
    { 'c', 4 }
};

listOfObjects.OrderBy(t => mapping[t.letter[0]]).ThenBy(t => t.id);

This has the benefit that it gives you absolute control over the order of those characters, and you can change the order externally, without having to change the actual order logic to handle exceptions.

Upvotes: 3

D Stanley
D Stanley

Reputation: 152624

Just reverse your first two conditions:

ListOfObjects.OrderBy(t => t.letter.StartsWith("c") ? 2 : 1)
             .ThenBy(t => t.letter)
             .ThenBy(t => t.id);

The first condition moves all cs to the end, then sorts by letter, then by id.

Since your first condition was already sorting by letter, trying to sort again based on letter had no effect.

Upvotes: 5

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