mergeByKey.js

// @flow
import { compose, objOf, mergeAll, map, view, lensProp } from 'ramda';

type MergeByKey = (key: string) => (Array<Object>) => Object;
/**
 * Provided a key, this function returns a function which merges an array of nested objects.
 * 
 * @example
 * // Given two objects:
 * const data1 = { key: { subStructure1: value1 } };
 * const data2 = { key: { subStructure2: value2 } };
 * 
 * // they can be merged together like the following:
 * mergeByKey('key')([data1, data2]);
 * // which results in { key: { subStructure1: value1, subStructure2: value2 }}
 * 
 * @param {*} key 
 */
export const mergeByKey: MergeByKey = key =>
  compose(
    // wrap result in the key
    objOf(key),
    // merge all objects together
    mergeAll,
    // extract objects from every input by the specific key
    map(view(lensProp(key))),
  );