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Asked: 2026-05-14T14:54:36+00:00

MSDN has no information on the order preserving properties of data structures. So I’ve

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MSDN has no information on the order preserving properties of data structures. So I’ve been making the assumption that:

  • HashTable and HashSet do not preserve the insertion order (i.e. the “hash” in there is a giveaway)
  • Dictionary and List do preserve the insertion order.

From this I extrapolate that if I have a Dictionary<double, double> foo that defines a curve, foo.Keys.ToList() and foo.Values.ToList() will give me an ordered list of the scope and domain of that curve without messing about with it?

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  1. Editorial Team

    You should NOT expect either the keys or values in a regular Dictionary<TKey,TValue> to be maintained in any order. In a SortedDictionary<TKey,TValue> the keys and values are maintained in order by the value of the key – this is not the same as insertion order.

    The only built-in dictionary in the .NET framework that preserves insertion order is System.Collections.Specialized.OrderedDictionary. Unfortunately, this class is not generic – however, it’s not terribly hard to write a generic wrapper around it. Keep in mind, when dealing with value types (like int or double) it will result in boxing of the keys/values (generic dictionaries don’t impose boxing on value types).

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