function pluck(collection, key) {
      return map(collection, property(key));
    }
Retrieves the value of a specified property from all elements in the collection.

@static
@memberOf _
@category Collection
@param {Array|Object|string} collection The collection to iterate over.
@param {string} key The name of the property to pluck.
@returns {Array} Returns the property values.
@example

var users = [
  { 'user': 'barney', 'age': 36 },
  { 'user': 'fred',   'age': 40 }
];

_.pluck(users, 'user');
// => ['barney', 'fred']

var userIndex = _.indexBy(users, 'user');
_.pluck(userIndex, 'age');
// => [36, 40] (iteration order is not guaranteed)