Adding #.multiplicity to MultiMap

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * Adding `#.has` to `FuzzyMap`.
 * Adding `#.has` to `FuzzyMultiMap`.
+* Adding `#.multiplicity` to `MultiMap`.
 * Renaming `RangeMap` to `IncrementalMap`.
 * Renaming `Index` to `FuzzyMap`.
 * Renaming `MultiIndex` to `FuzzyMultiMap`.

multi-map.js

@@ -108,6 +108,22 @@ MultiMap.prototype.get = function(key) {
   return this.items.get(key);
 };
 
+/**
+ * Method used to return the multiplicity of the given key, meaning the number
+ * of times it is set, or, more trivially, the size of the attached container.
+ *
+ * @param  {any}     key - Key to check.
+ * @return {number}
+ */
+MultiMap.prototype.multiplicity = function(key) {
+  var container = this.items.get(key);
+
+  if (typeof container === 'undefined')
+    return 0;
+
+  return this.Container === Set ? container.size : container.length;
+};
+
 /**
  * Method used to iterate over each of the key/value pairs.
  *

test/multi-map.js

@@ -27,6 +27,28 @@ describe('MultiMap', function() {
     assert.strictEqual(map.has('two'), false);
   });
 
+  it('should be possible to get the multiplicity of a key in the map.', function() {
+    var map = new MultiMap();
+
+    map.set('one', 'hello');
+    map.set('one', 'world');
+    map.set('two', 'test');
+
+    assert.strictEqual(map.multiplicity('three'), 0);
+    assert.strictEqual(map.multiplicity('one'), 2);
+    assert.strictEqual(map.multiplicity('two'), 1);
+
+    map = new MultiMap(Set);
+
+    map.set('one', 'hello');
+    map.set('one', 'hello');
+    map.set('two', 'test');
+
+    assert.strictEqual(map.multiplicity('three'), 0);
+    assert.strictEqual(map.multiplicity('one'), 1);
+    assert.strictEqual(map.multiplicity('two'), 1);
+  });
+
   it('should be possible to delete keys.', function() {
     var map = new MultiMap();