Group by flow

example.js

let data = _.flow(
  _.groupBy('country_id'),
  _.map(
    _.flow( // city group by level
      _.groupBy('city_id'),
      _.map(
        _.flow(   // person group by level
          _.groupBy('person_id'),
          _.map(vals => {
            return {
              children: _.flow(
                _.head,
                _.get('child_name')
                , vals),
              brothers: _.flow(
                _.head,
                _.get('brother_name')
                , vals),
              sisters: _.flow(
                _.head,
                _.get('sister_name')
                , vals),
            }
          }),
          _.object({
            city_id,
            city_field_1,
            city_field_2,
            people,       // from person group by level
          })
        ),
        _.object({
          country_id,
          country_field_1,
          country_field_2,
          people,       // from city group by level
        })
      )
    )
  )

promise.js

return getCountries()
.then(countries => {
  return Promise.all(countries.map(country => {
    return getCities(country)
      .then(cities => {
        return Promise.all(cities.map(city => {
          return getPeople(city)
            .then(people => {
              return map.people(async person => {
                return {
                  ...person,
                  children: await getChildren(person),
                  brothers: await getBrothers(person),
                  sisters: await getSisters(person),
                }
              })
            })
        }))
      }).then(cities_processed => {
        country.cities = cities_processed
        return country
      })
  })).then(countries_processed => {
    return {
      data: {
        countries: countries_processed
      }
    }
  })
})