Unigine::HashSet Class

A hash set container template. The hash set stores keys in an unspecified order. It allows for fast lookup of the keys. For example, you can implement fast searching among nodes by their IDs.

To create a new hash set, you can use the default constructor or one of the following ways:

• Create a hash set using an initializer list:
  Source code (C++)

  // constructor that takes an initializer list
  const HashSet<int> hashSet{ 4,7,2 };
  // check the result
  for (const auto &k : hashSet)
  	Log::message("%d ", k.key);

• Create a hash set using a copy constructor:
  Source code (C++)

  // constructor that takes an initializer list
  const HashSet<String> initial{ "a", "e" };
  // copy constructor
  const HashSet<String> expected(initial);
  // check the result
  for (const auto &k : expected)
  	Log::message("%s ", k.key.get());

• Create a new hash set by appending a vector of keys to it by using the fromKeys() function:
  Source code (C++)

  // create a vector of keys
  Vector<String> keys{ "1", "2", "3" };
  // append keys to an empty hash set
  HashSet<String> hashSet = HashSet<String>::fromKeys(keys);
  // check the result
  for (const auto &k : hashSet)
  	Log::message("%s ", k.key.get());

You can change the created hash set by using the class member functions described in the article. Check some of the usage examples:

• To add keys to the current hash set, you can use one of the append() or insert() functions:
  Source code (C++)

  // create hash sets using initializer lists
  HashSet<String> initial{ "a", "b", "c", "d", "e" };
  HashSet<String> to_add{ "m", "n", "o" };
  
  // append keys of the "to_add" hash set to the "initial" hash set
  initial.append(to_add);
  // insert a key into the "initial" hash set
  initial.insert("s");
  // check the result
  for (const auto &k : initial)
  	Log::message("%s ", k.key.get());

  Also it is possible to insert keys by using operator+=:
  Source code (C++)

  // create hash sets using initializer lists
  HashSet<String> initial{ "a", "e" };
  const HashSet<String> to_add{ "b", "c", "d" };
  const HashSet<String> expected{ "a", "b", "c", "d", "e" };
  
  // add one hash set to another
  initial += to_add;
  // check the result
  if (initial == expected) Log::message("The hash set has been added successfully\n");

  Notice

  If the key already exists in the hash set, it won't be added.
  Source code (C++)

  // create a hash set
  HashSet<String> set{ "s" };
  // assign one hash set to another
  const HashSet<String> original = set;
  
  // insert the hash set into the same hash set
  set.insert(set);
  // check the result - the hash set remains the same
  if (set == original) Log::message("Sets are equal\n");

  Source code (C++)

  // create an empty hash set
  HashSet<String> set;
  // create two equal strings
  const char *initial_str = "aaa";
  const String aaa0(initial_str), aaa1(initial_str);
  
  // add one of the strings as a key to the hash set
  set.insert(aaa0);
  // check the result
  if (set.contains(initial_str)) Log::message("The hash set contains the recently added key\n");
  Log::message("The size is %d\n", set.size());
  
  // add the duplicate string as a key to the hash set 
  set.insert(aaa1);
  // check the result - the size of the hash set remains the same
  Log::message("The size is %d\n", set.size());

• To remove keys from the hash set, you can use the subtract() or remove() function:
  Source code (C++)

  // create hash sets
  HashSet<String> initial{ "a", "b", "c", "d", "e" };
  const HashSet<String> to_subtract{ "a", "c", "e" };
  const HashSet<String> expected{ "b", "d" };
  
  // remove keys of one hash set from another
  initial.subtract(to_subtract);
  // check if the hash sets are equal
  if (initial == expected)  Log::message("Sets are equal\n");

  Source code (C++)

  // create hash sets
  HashSet<String> set{ "1", "2", "3", "4", "5" };
  HashSet<String> to_remove{ "3", "5" };
  
  // remove keys of one hash set from another
  set.remove(to_remove);
  // check the result
  for (const auto &k : set)
  	Log::message("%s ", k.key.get());

  Also the operator-= can be used:
  Source code (C++)

  // create hash sets
  HashSet<String> initial{ "a", "b", "c", "d", "e" };
  const HashSet<String> to_subtract{ "a", "c", "e" };
  const HashSet<String> expected{ "b", "d" };
  
  // remove keys of one hash set from another
  initial -= to_subtract;
  // check if the hash sets are equal
  if (initial == expected)  Log::message("Sets are equal\n");

• To clear the hash set, use the clear() function of the Hash class:
  Source code (C++)

  // create a hash set
  HashSet<String> set{ "1", "2", "3", "4", "5" };
  
  // remove all keys from the hash set
  set.clear();
  // check if the set is empty
  if (set.empty()) Log::message("The set is empty\n");