// https://d3js.org/d3-collection/ Version 1.0.1. Copyright 2016 Mike Bostock.
(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
  typeof define === 'function' && define.amd ? define(['exports'], factory) :
  (factory((global.d3 = global.d3 || {})));
}(this, function (exports) { 'use strict';

  var prefix = "$";

  function Map() {}

  Map.prototype = map.prototype = {
    constructor: Map,
    has: function(key) {
      return (prefix + key) in this;
    },
    get: function(key) {
      return this[prefix + key];
    },
    set: function(key, value) {
      this[prefix + key] = value;
      return this;
    },
    remove: function(key) {
      var property = prefix + key;
      return property in this && delete this[property];
    },
    clear: function() {
      for (var property in this) if (property[0] === prefix) delete this[property];
    },
    keys: function() {
      var keys = [];
      for (var property in this) if (property[0] === prefix) keys.push(property.slice(1));
      return keys;
    },
    values: function() {
      var values = [];
      for (var property in this) if (property[0] === prefix) values.push(this[property]);
      return values;
    },
    entries: function() {
      var entries = [];
      for (var property in this) if (property[0] === prefix) entries.push({key: property.slice(1), value: this[property]});
      return entries;
    },
    size: function() {
      var size = 0;
      for (var property in this) if (property[0] === prefix) ++size;
      return size;
    },
    empty: function() {
      for (var property in this) if (property[0] === prefix) return false;
      return true;
    },
    each: function(f) {
      for (var property in this) if (property[0] === prefix) f(this[property], property.slice(1), this);
    }
  };

  function map(object, f) {
    var map = new Map;

    // Copy constructor.
    if (object instanceof Map) object.each(function(value, key) { map.set(key, value); });

    // Index array by numeric index or specified key function.
    else if (Array.isArray(object)) {
      var i = -1,
          n = object.length,
          o;

      if (f == null) while (++i < n) map.set(i, object[i]);
      else while (++i < n) map.set(f(o = object[i], i, object), o);
    }

    // Convert object to map.
    else if (object) for (var key in object) map.set(key, object[key]);

    return map;
  }

  function nest() {
    var keys = [],
        sortKeys = [],
        sortValues,
        rollup,
        nest;

    function apply(array, depth, createResult, setResult) {
      if (depth >= keys.length) return rollup != null
          ? rollup(array) : (sortValues != null
          ? array.sort(sortValues)
          : array);

      var i = -1,
          n = array.length,
          key = keys[depth++],
          keyValue,
          value,
          valuesByKey = map(),
          values,
          result = createResult();

      while (++i < n) {
        if (values = valuesByKey.get(keyValue = key(value = array[i]) + "")) {
          values.push(value);
        } else {
          valuesByKey.set(keyValue, [value]);
        }
      }

      valuesByKey.each(function(values, key) {
        setResult(result, key, apply(values, depth, createResult, setResult));
      });

      return result;
    }

    function entries(map, depth) {
      if (++depth > keys.length) return map;
      var array, sortKey = sortKeys[depth - 1];
      if (rollup != null && depth >= keys.length) array = map.entries();
      else array = [], map.each(function(v, k) { array.push({key: k, values: entries(v, depth)}); });
      return sortKey != null ? array.sort(function(a, b) { return sortKey(a.key, b.key); }) : array;
    }

    return nest = {
      object: function(array) { return apply(array, 0, createObject, setObject); },
      map: function(array) { return apply(array, 0, createMap, setMap); },
      entries: function(array) { return entries(apply(array, 0, createMap, setMap), 0); },
      key: function(d) { keys.push(d); return nest; },
      sortKeys: function(order) { sortKeys[keys.length - 1] = order; return nest; },
      sortValues: function(order) { sortValues = order; return nest; },
      rollup: function(f) { rollup = f; return nest; }
    };
  }

  function createObject() {
    return {};
  }

  function setObject(object, key, value) {
    object[key] = value;
  }

  function createMap() {
    return map();
  }

  function setMap(map, key, value) {
    map.set(key, value);
  }

  function Set() {}

  var proto = map.prototype;

  Set.prototype = set.prototype = {
    constructor: Set,
    has: proto.has,
    add: function(value) {
      value += "";
      this[prefix + value] = value;
      return this;
    },
    remove: proto.remove,
    clear: proto.clear,
    values: proto.keys,
    size: proto.size,
    empty: proto.empty,
    each: proto.each
  };

  function set(object, f) {
    var set = new Set;

    // Copy constructor.
    if (object instanceof Set) object.each(function(value) { set.add(value); });

    // Otherwise, assume it’s an array.
    else if (object) {
      var i = -1, n = object.length;
      if (f == null) while (++i < n) set.add(object[i]);
      else while (++i < n) set.add(f(object[i], i, object));
    }

    return set;
  }

  function keys(map) {
    var keys = [];
    for (var key in map) keys.push(key);
    return keys;
  }

  function values(map) {
    var values = [];
    for (var key in map) values.push(map[key]);
    return values;
  }

  function entries(map) {
    var entries = [];
    for (var key in map) entries.push({key: key, value: map[key]});
    return entries;
  }

  exports.nest = nest;
  exports.set = set;
  exports.map = map;
  exports.keys = keys;
  exports.values = values;
  exports.entries = entries;

  Object.defineProperty(exports, '__esModule', { value: true });

}));