/**
 * Returns all of the property names (keys) of the specified object (a map). The
 * order of the returned array is not defined.
 *
 * @param map an object.
 * @returns {string[]} an array of strings corresponding to the keys.
 * @see #entries
 */
pv.keys = function(map) {
  var array = [];
  for (var key in map) {
    array.push(key);
  }
  return array;
};

/**
 * Returns all of the entries (key-value pairs) of the specified object (a
 * map). The order of the returned array is not defined. Each key-value pair is
 * represented as an object with <tt>key</tt> and <tt>value</tt> attributes,
 * e.g., <tt>{key: "foo", value: 42}</tt>.
 *
 * @param map an object.
 * @returns {array} an array of key-value pairs corresponding to the keys.
 */
pv.entries = function(map) {
  var array = [];
  for (var key in map) {
    array.push({ key: key, value: map[key] });
  }
  return array;
};

/**
 * Returns all of the values (attribute values) of the specified object (a
 * map). The order of the returned array is not defined.
 *
 * @param map an object.
 * @returns {array} an array of objects corresponding to the values.
 * @see #entries
 */
pv.values = function(map) {
  var array = [];
  for (var key in map) {
    array.push(map[key]);
  }
  return array;
};

/**
 * Returns a map constructed from the specified <tt>keys</tt>, using the
 * function <tt>f</tt> to compute the value for each key. The single argument to
 * the value function is the key. The callback is invoked only for indexes of
 * the array which have assigned values; it is not invoked for indexes which
 * have been deleted or which have never been assigned values.
 *
 * <p>For example, this expression creates a map from strings to string length:
 *
 * <pre>pv.dict(["one", "three", "seventeen"], function(s) s.length)</pre>
 *
 * The returned value is <tt>{one: 3, three: 5, seventeen: 9}</tt>. Accessor
 * functions can refer to <tt>this.index</tt>.
 *
 * @param {array} keys an array.
 * @param {function} f a value function.
 * @returns a map from keys to values.
 */
pv.dict = function(keys, f) {
  var m = {}, o = {};
  for (var i = 0; i < keys.length; i++) {
    if (i in keys) {
      var k = keys[i];
      o.index = i;
      m[k] = f.call(o, k);
    }
  }
  return m;
};