Sorting dictionary according to length of string values in C#

Question

Suppose I have a dictionary<int, string> like this

dict1 = {{[4,bcefgh]},{[5,abcefgh]},{[6,efgh]},{[7,bcefgh]},{[10,cefghi]}}

I want to sort pairs in this dictionary according to length of string values, without using extra loops. That is, results should be:

dict1 = {{[6,efgh]},{[4,bcefgh]},{[7,bcefgh]},{[10,cefghi]},{[5,abcefgh]}}

My initial answer was to create a separate dictionary that had the same keys and length of every corresponding string and a third dictionary that loops over pair as follows:

foreach (KeyValuePair<int,string> pair  in dict1)
{
    temp_dict.Add(pair.Key, pair.Value.Count());
}

var items = from pair in temp_dict
        orderby pair.Value ascending
            select pair;

foreach (KeyValuePair<int, int> pair in items)
{
    result_dict.Add(pair.Key, dict1[pair.Key]);
}

But this result is now practical with large set of data.

Not only it is impractical, it is incorrect. `Dictionary` doesn't preserve the order of items — Ilya Ivanov, Sep 03 '14 at 22:12

score 5 · Answer 1 · edited Sep 03 '14 at 22:12

5

You can't count on Dictionary being sorted. Instead you can use SortedDictionary<string, string> and pass its constructor a custom IComparer<T>.

edited Sep 03 '14 at 22:12

Grant Winney

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answered Sep 03 '14 at 22:09

brz

5,926
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`IComparer` in `SortedDictionary` takes `TKey`, not `TValue` http://stackoverflow.com/a/3417518/1283124 – Ilya Ivanov Sep 03 '14 at 22:10

Rufus L · Answer 2 · 2014-09-04T00:17:58.933

If you can live with an IOrderedEnumerable of KeyValuePairs, this will work:

var dict1 = new Dictionary<int, string>
{
    {4, "bcefgh"},
    {5, "abcefgh"},
    {6, "efgh"},
    {7, "bcefgh"},
    {10, "cefghi"}
};

IOrderedEnumerable<KeyValuePair<int, string>> sortedDict =
    dict1.OrderBy(i => i.Value.Length).ThenBy(i => i.Key);


foreach (var keyValuePair in sortedDict)
{
    Console.WriteLine(keyValuePair.Key + ": " + keyValuePair.Value);
}

// Output:
// 6: efgh
// 4: bcefgh
// 7: bcefgh
// 10: cefghi
// 5: abcefgh

score 0 · Answer 3 · answered Apr 19 '17 at 09:52

Here is what I use. A sorted set of key value pairs. Ordered by value length.

public class ValueSortedKeyValuePairSet : SortedSet<KeyValuePair <int, string>> 
    {

        private class StringLengthComparerDecending : IComparer<KeyValuePair <int, string>>
        {
            public int Compare(KeyValuePair <int, string> x, KeyValuePair <int, string> y)
            {
                var lengthComparison = x.Value.Length.CompareTo(y.Value.Length);
                return lengthComparison == 0 ? string.Compare(x.Value, y.Value, StringComparison.Ordinal) : lengthComparison;
            }
        }

        public ValueSortedKeyValuePairSet() : base(new StringLengthComparerDecending()) {}

        public ValueSortedKeyValuePairSet(IEnumerable<KeyValuePair <int, string>> e) : base(e, new StringLengthComparerDecending()) {}      
    }
}

Demo: https://dotnetfiddle.net/pklISX

Sorting dictionary according to length of string values in C#

3 Answers3