C# Case Insensitive Dictionary

Create a case-insensitive Dictionary with StringComparer.OrdinalIgnoreCase.

Case, Dictionary. A case-insensitive Dictionary is ideal in some programs. It helps with comparing file names in Windows, which ignore case.Dictionary

Notes, upper and lower. Sometimes user names are case-insensitive—upper and lower letters are treated as equal. We implement a case-insensitive string Dictionary.

An example. The Dictionary class has several overloaded constructors. Here we use one that accepts a parameter of type IEqualityComparer(string).

IEqualityComparer: This object implements an interface and is used by Dictionary to acquire hash codes and compare keys.

IEqualityComparer

New: We use a Dictionary constructor that accepts an IEqualityComparer. We specify StringComparer.OrdinalIgnoreCase as the comparer.

Methods: StringComparer.OrdinalIgnoreCase implements (at minimum) 2 methods, Equals and GetHashCode.

StringComparison, StringComparer

Info: These 2 methods are used internally by the Dictionary to compute hash keys and compare buckets.

C# program that uses case-insensitive Dictionary using System; using System.Collections.Generic; class Program { static void Main() { // Create case insensitive string Dictionary. var caseInsensitiveDictionary = new Dictionary<string, int>( StringComparer.OrdinalIgnoreCase); caseInsensitiveDictionary.Add("Cat", 2); caseInsensitiveDictionary.Add("Python", 4); caseInsensitiveDictionary.Add("DOG", 6); // Write value of "cat". Console.WriteLine(caseInsensitiveDictionary["CAT"]); // 2 // Write value of "PYTHON". Console.WriteLine(caseInsensitiveDictionary["PYTHON"]); // 4 // See if "dog" exists. if (caseInsensitiveDictionary.ContainsKey("dog")) { Console.WriteLine("Contains dog."); // <-- Displayed } // Enumerate all KeyValuePairs. foreach (var pair in caseInsensitiveDictionary) { Console.WriteLine(pair.ToString()); } } } Output 2 4 Contains dog. [Cat, 2] [Python, 4] [DOG, 6]

Notes, usage. You can add keys with either case using the Add method. The keys retain their original case internally in the Dictionary buckets.

And: When you enumerate the KeyValuePairs (in foreach), the original cases are retained.

Foreach

Caution: When you add the strings "Cat" and "CAT", you will get an exception. The Dictionary considers the 2 strings to be equivalent.

Note, ContainsKey. ContainsKey (along with TryGetValue) will accept keys of either case. So "PYTHON" will return the same value as "Python".ContainsKey TryGetValue

A discussion. Another approach you can use to normalize string data in your Dictionary is always calling ToLower on the keys and before looking up keys.ToLower

File names: In Windows, file names are case-insensitive. But when users copy files, they expect them to retain their original case.

Thus: This Dictionary is ideal here. It will mimic the behavior of Windows NTFS filesystems.

A summary. We implemented a case-insensitive string Dictionary. You do not need to write your own IEqualityComparer, although if your requirements are slightly unusual you can do so.

The Dev Codes

.Net

.NET Array Dictionary List String 2D Async DataTable Dates DateTime Enum File For Foreach Format IEnumerable If IndexOf Lambda LINQ Parse Path Process Property Regex Replace Sort Split Static StringBuilder Substring Switch Tuple

Java

Core Array ArrayList HashMap String 2D Cast Character Console Deque Duplicates File For Format HashSet If IndexOf Lambda Math ParseInt Process Random Regex Replace Sort Split StringBuilder Substring Switch Vector While

TheDeveloperBlog.com

C# Case Insensitive Dictionary

Related Links:

.Net

Java

Related Links