How to convert array of objects to array of arrays in javascript

Question

I have object of array of object. How to convert array of objects to array of arrays?

input = [
    {
        time: "2020-7",
        tasks: [
            {code: "p1", value: 1234},
            { code: "p2", value: 3445 },
        ]
    },
    {
        time: "2020-8",
        tasks: [
            { code: "p1", value: 3333 },
            { code: "p2", value: 4444 },
        ]
    }
]

I tried use forEach

let dataConvert=[], date=[],data=[];
input.forEach(x=>{
    return date = [...date, x.time]
})
console.log(date)
input.forEach(x=>{
    x.tasks.forEach(y=>{
        data = [...data,y.value]
    })
})
console.log(data);
dataConvert= [...dataConvert,date,data]

And get the results

dataConvert = [
    ["2020-7", "2020-8"],
    [1234, 3445, 3333, 4444]
]

I want the output looks like this:

output = [
    ["2020-7", "2020-8"],
    ["p1", 1234, 3333],
    ["p2", 3445, 4444],
]

Please help me.

You need to show your code and describe what was the problem. Please read How to Ask and how to create minimal reproducible example. — Yury Tarabanko
– Yury Tarabanko, Commented Aug 11, 2020 at 7:53

Karan · Accepted Answer · 2020-08-11 09:18:06Z

Try like below. Explanation is in comment.

let input = [
    {
        time: "2020-7",
        tasks: [
            {code: "p1", value: 1234},
            { code: "p2", value: 3445 },
        ]
    },
    {
        time: "2020-8",
        tasks: [
            { code: "p1", value: 3333 },
            { code: "p2", value: 4444 },
        ]
    }
];

// get array of time values.
let output = input.map(x => x.time);
// flatMap will create 1d array of tasks
// reduce will return object with key as code and value as an array of values for respective tasks.
let values = Object.values(input.flatMap(x => x.tasks).reduce((a, i) => {
  a[i.code] = a[i.code] || [i.code];
  a[i.code].push(i.value);
  return a;
}, {}));

// use spread operator to combine both values.
output = [output, ...values];

console.log(output);

@minhminh this is not the same structure because time elements are not inside an array. Please check my example

Krzysztof Kaczyński · Accepted Answer · 2020-08-11 09:19:09Z

This should work for you:

const input = [{
    time: "2020-7",
    tasks: [{
        code: "p1",
        value: 1234
      },
      {
        code: "p2",
        value: 3445
      },
    ]
  },
  {
    time: "2020-8",
    tasks: [{
        code: "p1",
        value: 3333
      },
      {
        code: "p2",
        value: 4444
      },
    ]
  }
];
const time = [];
const tasks = new Map();
for (const elem of input) {
  time.push(elem.time);
  for (const task of elem.tasks) {
    if (tasks.has(task.code)) {
      tasks.get(task.code).push(task.value.toString())
    } else {
      tasks.set(task.code, [task.value.toString()]);
    }
  }
}
const result = [time];
for (const [key, value] of tasks.entries()) {
  result.push([key, ...value]);
}
console.log(result);

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