Transform JSON to a predefined array of objects

Question

Given the JSON response below:

const result = {
  'potential': {
    A: 514,
    B: 3127,
    C: 2970,
    D: 282,
    E: 41,
    F: 1,
    undefined: 48,
  },
  'current': {
    A: 2,
    B: 961,
    C: 2897,
    D: 2568,
    E: 455,
    F: 47,
    G: 5,
    undefined: 48,
  },
};

I need to transform it to:

const temp = [
  { rating: 'A', potential: 514, current: 2 },
  { rating: 'B', potential: 3127, current: 961 },
  { rating: 'C', potential: 2970, current: 2897 },
  { rating: 'D', potential: 282, current: 2568 },
  { rating: 'E', potential: 41, current: 455 },
  { rating: 'F', potential: 1, current: 47 },
  { rating: 'G', potential: 0, current: 5 },
];

I manage by doing:

// Get unique list of keys
const allKeysSet = new Set(Object.keys(result).map(keys => Object.keys(result[keys])).flat().sort());

// Get feature names
const features = Object.keys(result);
const temp = [];

allKeysSet.forEach(s => {
  // Get features object with corresponding values, if undefined return 0
  const r = features.reduce((a, b) =>  ({ [a]: result[a][s] || 0, [b]: result[b][s] || 0 }));

  temp.push( { reference: s, ...r} );
});

console.log(temp);

If there is a simpler/efficient way of doing this, I'll appreciate it.

Answer 1

The first thing that can be useful to simplify your code is about the structure of the input data that contains almost the same keyset both in the potential and current properties, while the output contains the union of the two keysets. This suggests that Destructuring_assignment can help you to simplify your code, so you can unpack the potential and current properties of your initial data object into two different variables called potentialand current and obtain the union of the two keysets:

const {potential, current} = data; //<-- input data 
const allKeysSet = new Set(Object.keys(potential));
Object.keys(current).forEach(key => allKeysSet.add(key));

Your idea of using reduce and iterate over the keys of your data object is correct: you can transform your union keyset into an array with Array.from and can use the logical Nullish_coalescing_operator ?? to insert a default value (in your case 0):

const data = {
    'potential': {
      A: 514,
      B: 3127,
      C: 2970,
      D: 282,
      E: 41,
      F: 1,
    },
    'current': {
      A: 2,
      B: 961,
      C: 2897,
      D: 2568,
      E: 455,
      F: 47,
      G: 5,
    },
};
const {potential, current} = data;
const allKeysSet = new Set(Object.keys(potential));
Object.keys(current).forEach(key => allKeysSet.add(key));

const result = Array.from(allKeysSet).sort().reduce((acc, key) => {
    acc.push({'rating': key, 'potential': potential[key] ?? 0, 'current': current[key] ?? 0});
    return acc;
}, []);

console.log(result);

  

Answer 2

Combine two keys from potential & current store result in keys variable array using concat, Excluding undefined value by filter and with help of map create temp array:

const result = { 'potential': { A: 514, B: 3127, C: 2970, D: 282, E: 41, F: 1, undefined: 48, }, 'current': { A: 2, B: 961, C: 2897, D: 2568, E: 455, F: 47, G: 5, undefined: 48, }, };
const {potential:potentials, current:currents} = result;
const keys = [...new Set(Object.keys(potentials).concat(Object.keys(currents)))].filter(key=>key!='undefined'); // [ "A", "B", "C", "D", "E", "F", "G" ]
const temp = keys.map(key=>({rating:key,potential:potentials[key]??0,current:currents[key]??0}));
console.log(JSON.stringify(temp, null, 4))