How To Create Dictionary From String In Python

C# - Dictionary<TKey, TValue>

The Dictionary<TKey, TValue> is a generic collection that stores key-value pairs in no particular order.

Dictionary Characteristics

Dictionary<TKey, TValue> stores key-value pairs.
Comes under System.Collections.Generic namespace.
Implements IDictionary<TKey, TValue> interface.
Keys must be unique and cannot be null.
Values can be null or duplicate.
Values can be accessed by passing associated key in the indexer e.g. myDictionary[key]
Elements are stored as KeyValuePair<TKey, TValue> objects.

Creating a Dictionary

You can create the Dictionary<TKey, TValue> object by passing the type of keys and values it can store. The following example shows how to create a dictionary and add key-value pairs.

                          IDictionary<int,              string> numberNames =              new              Dictionary<int,              string>(); numberNames.Add(1,"One");              //adding a key/value using the Add() method              numberNames.Add(2,"Two"); numberNames.Add(3,"Three");              //The following throws run-time exception: key already added. //numberNames.Add(3, "Three");                            foreach(KeyValuePair<int,              string> kvp              in              numberNames)              Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);              //creating a dictionary using collection-initializer syntax              var              cities =              new              Dictionary<string,              string>(){ 	{"UK",              "London, Manchester, Birmingham"}, 	{"USA",              "Chicago, New York, Washington"}, 	{"India",              "Mumbai, New Delhi, Pune"} };              foreach(var              kvp              in              cities)              Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);

In the above example, numberNames is a Dictionary<int, string> type dictionary, so it can store int keys and string values. In the same way, cities is a Dictionary<string, string> type dictionary, so it can store string keys and string values. Dictionary cannot include duplicate or null keys, whereas values can be duplicated or null. Keys must be unique otherwise, it will throw a runtime exception.

Access Dictionary Elements

The Dictionary can be accessed using indexer. Specify a key to get the associated value. You can also use the ElementAt() method to get a KeyValuePair from the specified index.

                          var              cities =              new              Dictionary<string,              string>(){ 	{"UK",              "London, Manchester, Birmingham"}, 	{"USA",              "Chicago, New York, Washington"}, 	{"India",              "Mumbai, New Delhi, Pune"} };              Console.WriteLine(cities["UK"]);              //prints value of UK key              Console.WriteLine(cities["USA"]);//prints value of USA key              //Console.WriteLine(cities["France"]); // run-time exception: Key does not exist              //use ContainsKey() to check for an unknown key              if(cities.ContainsKey("France")){              Console.WriteLine(cities["France"]); }              //use TryGetValue() to get a value of unknown key              string              result;              if(cities.TryGetValue("France",              out              result)) {              Console.WriteLine(result); }              //use ElementAt() to retrieve key-value pair using index              for              (int              i = 0; i < cities.Count; i++) {              Console.WriteLine("Key: {0}, Value: {1}",                                              cities.ElementAt(i).Key,                                              cities.ElementAt(i).Value); }

Update Dictionary

Update the value of a key by specifying a key in the indexer. It will throw the KeyNotFoundException if a key does not exist in the dictionary, therefore use the ContainsKey() method before accessing unknown keys.

                          var              cities =              new              Dictionary<string,              string>(){ 	{"UK",              "London, Manchester, Birmingham"}, 	{"USA",              "Chicago, New York, Washington"}, 	{"India",              "Mumbai, New Delhi, Pune"} };  cities["UK"] =              "Liverpool, Bristol";              // update value of UK key              cities["USA"] =              "Los Angeles, Boston";              // update value of USA key              //cities["France"] = "Paris"; //throws run-time exception: KeyNotFoundException              if(cities.ContainsKey("France")){     cities["France"] =              "Paris"; }

Remove Elements in Dictionary

The Remove() method deletes an existing key-value pair from a dictionary. The Clear() method deletes all the elements of the dictionary.

                          var              cities =              new              Dictionary<string,              string>(){ 	{"UK",              "London, Manchester, Birmingham"}, 	{"USA",              "Chicago, New York, Washington"}, 	{"India",              "Mumbai, New Delhi, Pune"} };  cities.Remove("UK");              // removes UK                            //cities.Remove("France"); //throws run-time exception: KeyNotFoundException              if(cities.ContainsKey("France")){              // check key before removing it              cities.Remove("France"); }  cities.Clear();              //removes all elements