Get all keys in array of objects whose values are arrays

Question

I try to write all keys in an array of object whose values are arrays into a new array. Without duplicates. What is the best way in javascript, without libraries like lodash or underscore. I think that my solution is definitely improvable. The single objects and their keys are variable and not always identical. Suggestions welcome.

The intended output tom my example should be: [ "stuff", "type", "misc", "something" ]

const items = [{
    name: "Joe",
    occupied: "no",
    mobile: "yes",
    treatment: "no",
    date: "29-03-2020",
    age: "15",
    stuff: ["A", "B", "C"],
    type: ["1", "2"]
  },
  {
    name: "Jack",
    occupied: "yes",
    mobile: "no",
    treatment: "no",
    date: "02-03-2020",
    age: "20",
    stuff: ["A", "B", "C", "D", "E"],
    type: ["8", "6"],
    misc: ["otherStuff", "someStuff"]
  },
  {
    name: "Jane",
    occupied: "no",
    mobile: "yes",
    treatment: "yes",
    date: "15-02-2020",
    age: "28",
    stuff: ["C", "D", "E"],
    type: ["4", "7"],
    something: ["xxx", "ccc"]
  }
];


function getKeysWithArrayValues(myArray) {
  const result = [];
  myArray.forEach(item => Object.entries(item).forEach(itm => itm.filter(Array.isArray).forEach(x => result.push(itm.slice(0, 1)))));
  return flatArray(result)
};

function flatArray(array) {
  return array.reduce((acc, val) => Array.isArray(val) ? acc.concat(flatArray(val)) : acc.concat(val), []);
};
const ttt = getKeysWithArrayValues(items);
const flat = Array.from(new Set(ttt))
console.log(flat);

please add your solution.

Nina Scholz
– Nina Scholz

2020-03-29 21:05:53 +00:00
Commented Mar 29, 2020 at 21:05 — Nina Scholz
– Nina Scholz, Commented Mar 29, 2020 at 21:05
@nina edited code to runable snippet

Rambone
– Rambone

2020-03-29 21:14:58 +00:00
Commented Mar 29, 2020 at 21:14 — Rambone
– Rambone, Commented Mar 29, 2020 at 21:14

Tarukami · Accepted Answer · 2020-03-29 22:53:24Z

here is my solution, hope it helps. The algorithm is quite clear and I suppose there is no need to explan much. We just go through an array using reduce method and finally building the new array containing only keys that fit our requirements.

Array.isArray(rec[key]) checks if value is an array.

acc.indexOf(key) < 0 checks if the key has already been included into the resulting array on the one of previos steps.

const arr_ = items
  .reduce((acc, rec) => {
    return [...acc, ...Object.keys(rec).filter(key => Array.isArray(rec[key]) && acc.indexOf(key) < 0)]
  }, [])

Nina Scholz · Accepted Answer · 2020-03-29 21:18:31Z

You could take a Set and get unique keys of the objects.

const
    items = [{ name: "Joe", occupied: "no", mobile: "yes", treatment: "no", date: "29-03-2020", age: "15", stuff: ["A", "B", "C"], type: ["1", "2"] }, { name: "Jack", occupied: "yes", mobile: "no", treatment: "no", date: "02-03-2020", age: "20", stuff: ["A", "B", "C", "D", "E"], type: ["8", "6"], misc: ["otherStuff", "someStuff"] }, { name: "Jane", occupied: "no", mobile: "yes", treatment: "yes", date: "15-02-2020", age: "28", stuff: ["C", "D", "E"], type: ["4", "7"], something: ["xxx", "ccc"] }],
    keys = Array.from(
         items.reduce(
             (s, o) => Object
                  .keys(o)
                  .reduce((t, k) => Array.isArray(o[k]) ? t.add(k) : t, s),
             new Set
        )
    );

console.log(keys);

CertainPerformance · Accepted Answer · 2020-03-29 21:10:33Z

Use flatMap to iterate through each object's keys and return a filtered array of keys, on the condition of whether the value at that key is an array:

const items=[{name:"Joe",occupied:"no",mobile:"yes",treatment:"no",date:"29-03-2020",age:"15",stuff:["A","B","C"],type:["1","2"]},{name:"Jack",occupied:"yes",mobile:"no",treatment:"no",date:"02-03-2020",age:"20",stuff:["A","B","C","D","E"],type:["8","6"],misc:["otherStuff","someStuff"]},{name:"Jane",occupied:"no",mobile:"yes",treatment:"yes",date:"15-02-2020",age:"28",stuff:["C","D","E"],type:["4","7"],something:["xxx","ccc"]}];

const keysWithArrays = new Set(
  items.flatMap(
    item => Object.keys(item).filter(key => Array.isArray(item[key]))
  )
);
console.log([...keysWithArrays]);

Its syntax and operation have been standardized, and it's supported natively in all major browsers. It definitely will be part of the official language, I wouldn't call it experimental. For compatibility with old browsers, you can use a polyfill.

M A Salman · Accepted Answer · 2020-03-29 21:29:17Z

You can use set and Array.isArray() to check if value is array.

let mySet = new Set();    const items = [{name: "Joe",occupied: "no",mobile: "yes",treatment: "no",date: "29-03-2020",age: "15",stuff: ["A", "B", "C"],type: ["1", "2"]},{name: "Jack",occupied: "yes",mobile: "no",treatment: "no",date: "02-03-2020",age: "20",stuff: ["A", "B", "C", "D", "E"],type: ["8", "6"],misc: ["otherStuff", "someStuff"]
}, {name: "Jane",occupied: "no",mobile: "yes",treatment: "yes",date: "15-02-2020",age: "28",stuff: ["C", "D", "E"],type: ["4", "7"],something: ["xxx", "ccc"]}];

items.forEach((obj)=> Object.keys(obj).forEach( prop=>{if(Array.isArray(obj[prop])) 
mySet.add(prop)})); console.log(Array.from(mySet));

.as-console-wrapper { max-height: 100% !important; top: 0; }

Siva Kondapi Venkata · Accepted Answer · 2020-03-30 05:47:06Z

One more way with Object.fromEntries, flatMap and filter.

const items = [
  {
    name: "Joe",
    occupied: "no",
    mobile: "yes",
    treatment: "no",
    date: "29-03-2020",
    age: "15",
    stuff: ["A", "B", "C"],
    type: ["1", "2"]
  },
  {
    name: "Jack",
    occupied: "yes",
    mobile: "no",
    treatment: "no",
    date: "02-03-2020",
    age: "20",
    stuff: ["A", "B", "C", "D", "E"],
    type: ["8", "6"],
    misc: ["otherStuff", "someStuff"]
  },
  {
    name: "Jane",
    occupied: "no",
    mobile: "yes",
    treatment: "yes",
    date: "15-02-2020",
    age: "28",
    stuff: ["C", "D", "E"],
    type: ["4", "7"],
    something: ["xxx", "ccc"]
  }
];

const keys = Object.keys(
  Object.fromEntries(
    items.flatMap(item =>
      Object.entries(item).filter(([, value]) => Array.isArray(value))
    )
  )
);

console.log(keys);

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