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Dictionaries

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How to create an instance of Dictionary<TKey, TValue> with preset values?​

Classic approach
var dic = new Dictionary<string, string> 
{
  { "key 1", "value 1" },
  { "key 2", "value 2" },
  { "key 3", "value 3" },
};
C# 6.0 and above
var dic = new Dictionary<string, string> 
{
  ["key 1"] = "value 1",
  ["key 2"] = "value 2",
  ["key 3"] = "value 3",
};

How to make keys case-insensitive?​

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

How to merge two dictionaries?​

var dictionaryA = new Dictionary<string, string>
{
  { "key_1", "value_1" },
  { "key_2", "value_2" },
};

var dictionaryB = new Dictionary<string, string>
{
  { "key_3", "value_3" },
  { "key_4", "value_4" },
};

var merged = dictionaryA.Concat(dictionaryB).ToDictionary(x => x.Key, x => x.Value);

Console.WriteLine(merged["key_1"]); // value_1
Console.WriteLine(merged["key_4"]); // value_4

What is better: Dictionary or Hashtable?​

In the vast majority of cases, it is recommended to use Dictionary<TKey, TValue>.

Dictionary<TKey, TValue> is simpler, more reliable, and works faster.