How to combine multiple JSON objects where key value is the same

Question

I'm trying to combine objects which share the same module key value, i.e. "credit cards". I need to return a single object per unique module with an array of distinct companies. The id and prod keys aren't important.

Here's the object I need to transform:

const data = [
   {module: "credit_cards", id: "1", company: "ABC", prod: "1"}, 
   {module: "credit_cards", id: "2", company: "XYZ", prod: "2"}, 
   {module: "credit_cards", id: "3", company: "EFG", prod: "2"}, 
   {module: "credit_cards", id: "2", company: "XYZ", prod: "2"}, 
   {module: "mortgages", id: "4", company: "EFG", prod: "3"}
]

I need to return something like this:

const result = [
{module: "credit_cards", company: ["ABC", "XYZ", "EFG"]}, 
{module: "mortgages", company: ["EFG"]}
]

So far, I've tried this function:

const result = data.reduce(function(r, e) {
  return Object.keys(e).forEach(function(k) {
    if(!r[k]) r[k] = [].concat(e[k])
    else r[k] = r[k].concat(e[k])
  }), r
}, {})

But it just concatenated all the key/values together...

Any help would be awesome, thanks :)

Answer 1

You can use first Array.reduce() to group the companies by the module key on a Set. On a second step you can use array.Map() over the generated object .entries() to get the final desired result:

const data = [
   {module: "credit_cards", id: "1", company: "ABC", prod: "1"}, 
   {module: "credit_cards", id: "2", company: "XYZ", prod: "2"}, 
   {module: "credit_cards", id: "3", company: "EFG", prod: "2"}, 
   {module: "credit_cards", id: "2", company: "XYZ", prod: "2"}, 
   {module: "mortgages", id: "4", company: "EFG", prod: "3"}
];

let res = data.reduce((acc, {module, company}) =>
{
    acc[module] = acc[module] || new Set();
    acc[module].add(company);
    return acc;
}, {})

res = Object.entries(res).map(
    ([module, companies]) => ({module, company: [...companies]})
);

console.log(res);

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