code: public final <K extends Comparable<? super K>> Ix<T> orderBy(IxFunction<? super T, K> keySelector) {
          return new IxOrderBy<T, K>(this, nullCheck(keySelector, "keySelector is null"), SelfComparator.INSTANCE, 1);
      }
docs: Orders elements according to the natural order of the extracted keys from these elements.
  <p>
  The result's iterator() doesn't support remove().
  @param <K> the key type
  @param keySelector the function receiving each element and returns a self-comparable key for them.
  @return the new Ix instance
  @throws NullPointerException if keySelector is null
  @since 1.0
  @see #orderByReverse(IxFunction)