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up vote 1 down vote favorite

Say I have the following 2 arrays

string[] keys = new string[]{"Annalee Call","Bishop","Ash"};

MyClass[] vals = new MyClass[]{
    new MyClass(){name = "Ash"},
    new MyClass(){name = "Annalee Call"},
    new MyClass(){name = "Bishop"}
};

What is the best way to sort the MyClass array by name based on the keys array without resorting to for loops?

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2 Answers 2

up vote 3 down vote accepted

One way to do it would be as follows:

var sorted = vals.OrderBy(s => Array.IndexOf(keys, s.name)).ToArray();

Note that this algorithm is asymptotically very slow: it has O(N^2*LogN) complexity. To bring it back to the "normal" O(N*LogN), prepare a lookup dictionary for finding indexes, like this:

var keyDict = keys.Select((v,i)=>new {v,i}).ToDictionary(p=>p.v, p=>p.i);
var sorted = vals.OrderBy(s => keyDict[s.name]).ToArray();
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This worked perfectly, thank you for the additional information and providing the lookup dictionary. –  opdb Aug 13 '13 at 2:38
up vote 1 down vote

I would use this approach to do the sorting. It handles the case if values in vals are missing from the keys list.

var rank =
    keys
        .Select((v, n) => new { Value = v, Rank = n, })
        .ToLookup(vn => vn.Value, vn => vn.Rank);

var query =
    from v in vals
    orderby rank[v.name]
        .DefaultIfEmpty(int.MaxValue)
        .First()
    select v;

Otherwise it is very similar to dasblinkenlight's answer.

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You make a good point in checking for the existence of each key. In my current situation a check is not needed, but pretty much every other scenario should implement a key check. –  opdb Aug 13 '13 at 2:58

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