code: function mapFromArray(array, prop) {
        var map = {};
        for (var i = 0; i < array.length; i++) {
          map[ array[i][prop] ] = array[i];
        }
        return map;
      }
docs: Creates a map out of an array be choosing what property to key by
  @param {object[]} array Array that will be converted into a map
  @param {string} prop Name of property to key by
  @return {object} The mapped array. Example:
  mapFromArray([{a:1,b:2}, {a:3,b:4}], 'a')
  returns {1: {a:1,b:2}, 3: {a:3,b:4}}