This is a feature request. Something like this:

create_map(
  ['cat', 'bear', 'aardvark'],
  function($element, $index, $collection) {
    return strlen($element);
  }
);
/*
returns [
  'cat'=>3,
  'bear'=>4,
  'aardvark'=>8
];
*/

I'm not sure what that function would be called, I admit that it should have a better name than create_map

Couldn't properly explain what I want in the original post, see a comment below: #164 (comment)