function wrapperToString() {
      return (this.value() + '');
    }
Creates an array of elements corresponding to the given keys, or indexes,
of `collection`. Keys may be specified as individual arguments or as arrays
of keys.

@static
@memberOf _
@category Collection
@param {Array|Object|string} collection The collection to iterate over.
@param {...(number|number[]|string|string[])} [props] The property names
 or indexes of elements to pick, specified individually or in arrays.
@returns {Array} Returns the new array of picked elements.
@example

_.at(['a', 'b', 'c'], [0, 2]);
// => ['a', 'c']

_.at(['barney', 'fred', 'pebbles'], 0, 2);
// => ['barney', 'pebbles']