// ========
// Usage
// ========
// > const { transposeObjects } = require('./utils');
// undefined
// > transposeObjects([
// ... { key1: 'object1key1', key2: 'object1key2' },
// ... { key1: 'object2key1', key2: 'object2key2' }
// ... ])
// { key1: [ 'object1key1', 'object2key1' ],
//   key2: [ 'object1key2', 'object2key2' ] }

const R = require('ramda');

const lensPropWithDefault = R.curry((defaultValue, key) => {
  return R.lens(R.propOr(defaultValue, key), R.assoc(key));
});

const transposeObjects = (objects) => {
  const appendProperty = R.curry((object, acc, key) => {
    return R.over(
      lensPropWithDefault([], key),
      R.append(R.prop(key, object)),
      acc
    );
  });

  const appendProperties = (acc, object) => {
    return R.reduce(appendProperty(object), acc, R.keys(object));
  };

  return R.reduce(appendProperties, {}, objects);
};