title: With parallel collection, does aggregate respect order?
body: <p>in scala, i have a parallel Iterable of items and i want to iterate over them and aggregate the results in some way, but in order. i'll simplify my use case and say that we start with an Iterable of integers and want to concatenate the string representation of them in paralle, with the result in order.</p>
  
  <p>is this possible with either fold or aggregate? it's unclear from the documentation which methods work parallelized but maintain order.</p>