隔离嵌套数组中的数组元素，并将其用作JSON字段值，并将其同级数组元素用作字段值

Question

My question is about isolating an array element inside nested array and use it as the JSON field value with it's sibling array elements as a field value properties.

My Array:

"S,No.", "id", "date", "time"

eachArray = [
    ["1", "4", "2018/07/05", "22:27:35"],
    ["2", "1", "2018/07/05", "22:28:02"],
    ["3", "3", "2018/07/22", "21:25:51"],
    ["4", "3", "2018/07/22", "21:25:59"],
    ["5", "2", "2018/07/22", "21:25:59"],
    ["6", "1", "2018/07/25", "22:36:55"],
    ["7", "1", "2018/07/25", "21:25:51"],
]

---

I want to make a JSON object with the format like:

jsonArray = {
    "2018/07/05" : ["4","1"],
    "2018/07/22" : ["3","2"],
    "2018/07/25" : ["1"]
}

---

My attempt so far:

 eachArray = [ ["1", "4", "2018/07/05", "22:27:35"], ["2", "1", "2018/07/05", "22:28:02"], ["3", "3", "2018/07/22", "21:25:51"], ["4", "3", "2018/07/22", "21:25:59"], ["5", "2", "2018/07/22", "21:25:59"], ["6", "1", "2018/07/25", "22:36:55"], ["7", "1", "2018/07/25", "21:25:51"], ] var outerSet = []; var jsonArray = {}; eachArray.forEach((val, index) =>{ var outerLast = outerSet.pop(); var set = eachArray[index][1]; var dateHere = eachArray[index][3]; outerSet.push(set); if(index !== 0){ if(outerLast !== dateHere){ outerSet = []; jsonArray[dateHere] = set; return; } } outerSet.push(dateHere); jsonArray[dateHere] = outerSet; }); 

Answer 1

Try reduce -ing into an object indexed by date, whose values are Set s (to deduplicate), to which you add the number in each item, and then once you've gone through the eachArray , convert the Set s back to arrays:

 const eachArray = [ ["1", "4", "2018/07/05", "22:27:35"], ["2", "1", "2018/07/05", "22:28:02"], ["3", "3", "2018/07/22", "21:25:51"], ["4", "3", "2018/07/22", "21:25:59"], ["5", "2", "2018/07/22", "21:25:59"], ["6", "1", "2018/07/25", "22:36:55"], ["7", "1", "2018/07/25", "21:25:51"], ] const itemsByDate = eachArray.reduce((a, [, num, date]) => { if (!a[date]) a[date] = new Set(); a[date].add(num); return a; }, {}); Object.entries(itemsByDate).forEach(([key, set]) => { itemsByDate[key] = [...set]; }); console.log(itemsByDate); 

Answer 2

You can also use a plain object to store date as key and values as a Set . Values should be stored on a set so that it won't have duplicates. Then at the end, convert all the Sets to Arrays using Array.from function.

eachArray = [
    ["1", "4", "2018/07/05", "22:27:35"],
    ["2", "1", "2018/07/05", "22:28:02"],
    ["3", "3", "2018/07/22", "21:25:51"],
    ["4", "3", "2018/07/22", "21:25:59"],
    ["5", "2", "2018/07/22", "21:25:59"],
    ["6", "1", "2018/07/25", "22:36:55"],
    ["7", "1", "2018/07/25", "21:25:51"],
];

var obj = {};
eachArray.forEach(arr => {
    if(!obj[arr[2]]){
        obj[arr[2]] = new Set();
    }
    obj[arr[2]].add(arr[1]);
});
Object.keys(obj).forEach(key => obj[key] = Array.from(obj[key]));
console.log(obj);

Answer 3

 const input = [ ["1", "4", "2018/07/05", "22:27:35"], ["2", "1", "2018/07/05", "22:28:02"], ["3", "3", "2018/07/22", "21:25:51"], ["4", "3", "2018/07/22", "21:25:59"], ["5", "2", "2018/07/22", "21:25:59"], ["6", "1", "2018/07/25", "22:36:55"], ["7", "1", "2018/07/25", "21:25:51"], ]; const output = input.reduce((accu, [, num2, date,]) => { if(!accu[date]) accu[date] = []; if(!accu[date].includes(num2)) accu[date].push(num2); return accu; }, {}); console.log(output);