View Category
Maps
Declaration

Define an empty map

cpp
Hashtable^ hash = gcnew Hashtable;
Generic::Dictionary<String^, String^>^ dict = gcnew Generic::Dictionary<String^, String^>();
std::map<int, std::string> m;

Define an unmodifiable empty map

Define an initial map

Define the map {circle:1, triangle:3, square:4}
cpp
Hashtable^ shapes = gcnew Hashtable;

shapes->Add("circle", 1);
shapes->Add("triangle", 3);
shapes->Add("square", 4);
Generic::Dictionary<String^, int>^ shapes = gcnew Generic::Dictionary<String^, int>();

shapes->Add("circle", 1);
shapes->Add("triangle", 3);
shapes->Add("square", 4);
Access

Check if a key exists in a map

Given a map pets {joe:cat,mary:turtle,bill:canary} print "ok" if an pet exists for "mary"
cpp
if (pets->ContainsKey("mary")) Console::WriteLine("ok");
if (pets.find("mary") != pets.end()){
std::cout << "ok" << std::endl;
}

Retrieve a value from a map

Given a map pets {joe:cat,mary:turtle,bill:canary} print the pet for "joe" ("cat")
cpp
if (pets->ContainsKey("joe")) Console::WriteLine(pets["joe"]);

Add an entry to a map

Given an empty pets map, add the mapping from "rob" to "dog"
cpp
pets->Add("rob", "dog");
pets["rob"] = "dog";

Remove an entry from a map

Given a map pets {joe:cat,mary:turtle,bill:canary} remove the mapping for "bill" and print "canary"
cpp
if (pets->ContainsKey("bill"))
{
String^ value = safe_cast<String^>(pets["bill"]); pets->Remove("bill");
Console::WriteLine("{0}", value);
}
Algorithms

Create a histogram map from a list

Given the list [a,b,a,c,b,b], produce a map {a:2, b:3, c:1} which contains the count of each unique item in the list
cpp
for each(String^ entry in input) hash[entry] = hash->ContainsKey(entry)
? Convert::ToInt32(hash[entry]->ToString()) + 1 : 1;
for each(String^ entry in input) dict[entry] = dict->ContainsKey(entry) ? dict[entry] + 1 : 1;

Categorise a list

Given the list [one, two, three, four, five] produce a map {3:[one, two], 4:[four, five], 5:[three]} which sorts elements into map entries based on their length
cpp
for each(String^ entry in input)
{
key = entry->Length;
if (!hash->ContainsKey(key)) hash[key] = gcnew ArrayList;
safe_cast<ArrayList^>(hash[key])->Add(entry);
}