Selecting fields in query with preloaded data

How can I select fields and add custom fields in Repo.all query with preloaded data.

I have this query

    Repo.all from p in EmployeeProfile,
    join: c in assoc(p, :employee_checklists),
    preload: [employee_checklists: c],
    select: [:name, :id],
    select_merge: %{total_checklist_items: count(c)},
    group_by: [p.id, c.id]

When executed the results are below: (a)

[
  %{
    total_checklist_items: 1,
    employee_checklists: [
      %Prepply.Employees.EmployeeChecklist{
        __meta__: #Ecto.Schema.Metadata<:loaded, "employee_checklists">,
        checklist_item: #Ecto.Association.NotLoaded<association :checklist_item is not loaded>,
        checklist_item_id: 2,
        employee_profile: #Ecto.Association.NotLoaded<association :employee_profile is not loaded>,
        employee_profile_id: 3,
        file_path: nil,
        id: 2,
        inserted_at: ~N[2020-12-29 10:33:10],
        status: "completed",
        updated_at: ~N[2020-12-29 10:33:10]
      },
      %Prepply.Employees.EmployeeChecklist{
        __meta__: #Ecto.Schema.Metadata<:loaded, "employee_checklists">,
        checklist_item: #Ecto.Association.NotLoaded<association :checklist_item is not loaded>,
        checklist_item_id: 1,
        employee_profile: #Ecto.Association.NotLoaded<association :employee_profile is not loaded>,
        employee_profile_id: 3,
        file_path: nil,
        id: 1,
        inserted_at: ~N[2020-12-29 10:33:10],
        status: "",
        updated_at: ~N[2020-12-29 10:33:10]
      }
    ],
    id: 3,
    name: "..."
  }
]

but what I want to achieve is something like this: (b)

[
  %{
    total_checklist_items: 2,
    completed_checklists: 1 (if one of CheckListItem struct has status = "completed"
    id: 3,
    name: "..."
  }
]

how can I achieve something like (b)?