Sort Dictionary<> on value, lookup index from key

Question

Hi,

I have a Dictionary<> which I want to sort based on value so I've done this by putting the dictionary into a List<> then using the .Sort method.

I've then added this back into a Dictionary<>. Is it possible to lookup the new index/order by using the Dictionary key??

Dictionary<int, MyObject> toCompare = new Dictionary<int, MyObject>();

toCompare.Add(0, new MyObject());
toCompare.Add(1, new MyObject());
toCompare.Add(2, new MyObject());

Dictionary<int, MyObject> items = new Dictionary<int, MyObject>();
List<KeyValuePair<int, MyObject>> values = new List<KeyValuePair<int, MyObject>>   (toCompare);

// Sort.
values.Sort(new MyComparer());

// Convert back into a dictionary.
foreach(KeyValuePair<int, PropertyAppraisal> item in values)
{
      // Add to collection.
  items.Add(item.Key, item.Value);
}

// THIS IS THE PART I CAN'T DO...
int sortedIndex = items.GetItemIndexByKey(0);

Answer 1

Keep your data in the Dictionary<TKey,TValue>, but use a List<TKey> to sort the keys, then iterate as such:

IDictionary<int, MyObject> dict = new Dictionary<int, MyObject>();
// ... Populate dict with data.

IList<int> keyList = new List<int>();
keyList.AddRange(dict.Keys);

// Sort keyList based on key's value.
// MyObject must implement IComparable<MyObject>.
keyList.Sort(delegate(int x, int y) {
   return dict[x].CompareTo(dict[y]);
});

foreach (int key in keyList) {
   MyObject value = dict[key];
}

This way, your list is merely a sorted index and does not affect your storage algorithm.

Answer 2

Take this extension method:

public static Dictionary<TKey, TValue> Sort<TKey, TValue, TSortingKey>(this Dictionary<TKey, TValue> source, 
    Func<KeyValuePair<TKey, TValue>, TSortingKey> selector)
{
    var result = new Dictionary<TKey, TValue>();
    foreach (var pair in source.OrderBy(selector))
        result.Add(pair.Key, pair.Value);
    return result;
}

And usage:

    Dictionary<int, MyType> source = new Dictionary<int, MyType>();
    Dictionary<int, MyType> sortedDictionary = source.Sort(i => i.Value.Property1); //sort dictionary by values (by property "Property1" of type MyType

Hope this helps