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());
}
}
}
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.
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.