vertical_with_comments.js

  const sizeDifference    = _(proposals).size() - _(definedUserAnswers).size(); // 2
  const arrayOfFalse = _.times(sizeDifference, _.constant(false));              // [false, false]

  return  _.chain(definedUserAnswers) // [false, true]
            .concat(arrayOfFalse)     // [false, true, false, false]
            .zip(proposals)           // [[false, 'prop 1'], [true, 'prop 2'], [false, 'prop 3'], [false, 'prop 4']]
            .map(_.reverse)           // [['prop 1', false], ['prop 2', true], ['prop 3', false], ['prop 4', false]]
            .value();