nest.key(key) Registers a new key function. The key function will be invoked for each element in the

nest.object(array) Applies the nest operator to the specified array, returning a nested object. Each entry

d3.entries(object) Returns an array containing the property keys and values of the specified object (an associative array).

d3.keys(object) Returns an array containing the property names of the specified object (an associative array). The order of

d3.set([array[, accessor]]) Constructs a new set. If array is specified, adds the given array of string

set.each(function) Calls the specified function for each value in this set, passing the value as the first

map.get(key) Returns the value for the specified key string. If the map does not have an entry for the specified

d3.map([object[, key]]) Constructs a new map. If object is specified, copies all enumerable properties from

map.entries() Returns an array of key-value objects for each entry in this map. The order of the returned entries is arbitrary

map.empty() Returns true if and only if this map has zero entries.