How to transform JavaScript object values into array

Question

I need to write a function to transform an object like this:

const foodList = {fruit: {apples: true, pears: false, berries: true}, dairy: {milk: true, cheese: false}, vegetables: {}}
console.log(foodList)

into this:

const result = {fruit: ['apples', 'berries'], dairy: ['milk']}
console.log(result)

I'm trying to convert the nested values to an array where the food key equals true.

From where the property deposits come from, should not be dairy? Also, there is no JSON object, that is just a javascript object. A JSON is a string notation for an object. — Shidersz
– Shidersz, Commented May 22, 2019 at 2:51

Eddie · Accepted Answer · 2019-05-22 02:55:35Z

3

You can use Object.entries to convert the object into an array. Use reduce to loop and summarize the array. Use Object.keys and filter to get the keys with true value.

const foodList = {"fruit":{"apples":true,"pears":false,"berries":true},"dairy":{"milk":true,"cheese":false},"vegetables":{}}

const result = Object.entries(foodList).reduce((c, [k, v]) => {
  let t = Object.keys(v);
  if (t.length) c[k] = t.filter(o => v[o]);
  return c;
}, {});

console.log(result);

answered May 22, 2019 at 2:55

Eddie

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Comments

Shidersz · Accepted Answer · 2019-05-22 03:21:26Z

Another alternative to get the desired output is to use two nested for loops to traverse the outer and the inner keys while generating the resulting object. This way, you can also avoid to generate a property on the resulting object if all the elements inside a category have the false value.

const foodList = {
  fruit: {apples: true, pears: false, berries: true},
  dairy: {milk: true, cheese: false},
  vegetables: {},
  food: {hamburger: false, spaghetti: false}
};

let res = {};

for (const category in foodList)
{
    for (const item in foodList[category])
    {
        if (foodList[category][item])
        {
            res[category] = res[category] || [];
            res[category].push(item);
        }
    }
}

console.log(res);

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