lagrangian_set_Recycle Subroutine

    pure subroutine lagrangian_set_Recycle(this)
      !> Sorting routine: stacks active lagrangian
      ! objects (i.e., who's id is >=1) at the beginning of
      ! the array then resizes. Objects with id <= 0 (such as
      ! ghost objects) are removed by this subroutine.
      implicit none
      class(lagrangian_set), intent(inout) :: this                             !! A set of Lagrangian objects
      ! Work variables
      integer :: count_active                                                  !! Number of active objects
      integer :: i                                                             !! iterator

      count_active = 0
      if (allocated(this%p)) then
        do i=1,size(this%p)
          if (this%p(i)%id.gt.0) then
            count_active = count_active + 1
            if (i.ne.count_active) then
              ! Move back the object
              this%p(count_active)=this%p(i)

              ! Set current position inactive
              this%p(i)%id = -1
            end if
          end if
        end do
      end if

      ! Resize array to count_active
      call this%Resize(count_active)

      return
    end subroutine lagrangian_set_Recycle