CODEWITHSUNDEEP
c#.netgenericsdictionarycase-insensitive
WillHart
WillHart

Reputation: 75

Make an existing Dictionary case insensitive .Net

I know how to make a new dictionary case insensitive with the code below:

var caseInsensitiveDictionary = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);

But I'm using WebApi which serializes JSON objects into a class we've created.

public class Notification : Common
{
    public Notification();

    [JsonProperty("substitutionStrings")]
    public Dictionary<string, string> SubstitutionStrings { get; set; }
}

So besides rebuilding the dictionary after receiving the "Notification" object, is there a way to set this dictionary to case insensitive in the first place or after it's been created?

Thanks

Upvotes: 4

Views: 1922

Answers (4)

stvo
stvo

Reputation: 41

You do have to re-create the dictionary, but this can be done with extensions:

public static class extensions
{
    public static Dictionary<string, T> MakeCI<T>(this Dictionary<string, T> dictionary)
    {
        return dictionary.ToDictionary(kvp => kvp.Key, kvp => kvp.Value, StringComparer.OrdinalIgnoreCase);
    }
}

I've specified string type for the key as this is what we want to be CI, but the value can be any type.

You would use it like so:

myDict = myDict.MakeCI();

Upvotes: 1

Nicholas Carey
Nicholas Carey

Reputation: 74267

Try changing your class definition to something like this

public class Notification : Common
{
  public Notification()
  {
    this.substitutionStringsBackingStore =
       new Dictionary<string,string>( StringComparer.OrdinalIgnoreCase )
       ; 
  }

  [JsonProperty("substitutionStrings")]
  public Dictionary<string, string> SubstitutionStrings
  {
    get { return substitutionStringsBackingStore         ; }
    set {        substitutionStringsBackingStore = value ; }
  }
  private Dictionary<string,string> substitutionStringsBackingStore ;
}

Upvotes: 1

supercat
supercat

Reputation: 81159

Whenever an item is added to a dictionary, the dictionary will compute its hash code and make note of it. Whenever a dictionary is asked to look up an item, the dictionary will compute the hash code on the item being sought and assume that any item in the dictionary which had returned a different hash code cannot possibly match it, and thus need not be examined.

In order for a dictionary to regard "FOO", "foo", and "Foo" as equal, the hash code function it uses must yield the same value for all of them. If a dictionary was built using a hash function which returns different values for "FOO", "foo", and "Foo", changing to a hash function which yielded the same value for all three strings would require that the dictionary re-evaluate the hash value of every item contained therein. Doing this would require almost as much work as building a new dictionary from scratch, and for that reason .NET does not support any means of changing the hash function associated with a dictionary other than copying all the items from the old dictionary to a new dictionary, abandoning the old one.

Note that one could design a SwitchablyCaseSensitiveComparator whose GetHashCode() method would always return a case-insensitive hash value, but whose Equals method could be switched between case-sensitive and non-case sensitive operation. If one were to implement such a thing, one could add items to a dictionary and then switch between case-sensitive and non-case-sensitive modes. The biggest problem with doing that would be that adding if the dictionary is in case-sensitive mode when two items are added which differ only in case, attempts to retrieve either of those items when the dictionary is in case-insensitive mode might not behave as expected. If populating a dictionary in case-insensitive mode and performing some look-ups in case-sensitive mode should be relatively safe, however.

Upvotes: 1

Servy
Servy

Reputation: 203829

So besides rebuilding the dictionary after receiving the "Notification" object, is there a way to set this dictionary to case insensitive in the first place or after it's been created?

No, it is impossible. You need to create a new dictionary.

Currently the dictionary has all of the keys in various different buckets; changing the comparer would mean that a bunch of keys would all suddenly be in the wrong buckets. You'd need to go through each key and re-compute where it needs to go and move it, which is basically the same amount of work as creating a new dictionary would be.

Upvotes: 5

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