Convert array of object arrays to a single array in JavaScript [closed]

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I have an array of objects having multiple arrays

 const arr =  [
    {
        JUNE: [
            {
                "iD": "67854",
                "event": " closed",
                "title": "test",
                "startDate": "2024-06-20",
                "endDate": "2024-07-25"
            }
        ]
    },
    {
        MAY: [
            {
                "ID": "908765",
                "event": "closed",
                "title": "test",
                "startDate": "2024-05-21",
                "endDate": "2024-06-27"
            },
            {
                ID: "12345",
                event: "open",
                title: "test123",
                startDate: "2024-05-21",
                endDate: "2024-06-27"
            }
        ]
    }
]

Output I need

   [
    {
        ID: "67854",
        event: "closed",
        title: "test",
        startDate: "2024-06-20",
        endDate: "2024-07-25"
    },
    {
        ID: "908765",
        event: "closed",
        title: "test",
        startDate: "2024-05-21",
        endDate: "2024-06-27"
    },
    {
        ID: "12345",
        event: "open",
        title: "test123",
        startDate: "2024-05-21",
        endDate: "2024-06-27"
    }

]

Looks an awful lot like Flattening deeply nested array of objects or How to flatten the nested array of of objects and duplicate the parent — Heretic Monkey
– Heretic Monkey, Commented Apr 1, 2024 at 21:48
Yea well if you dont need the months you can get that with a reduce and map on Object.values. Again, please show us your attempt. — 0stone0
– 0stone0, Commented Apr 1, 2024 at 21:54

Alexander Nenashev · Accepted Answer · 2024-04-01 22:41:45Z

2

arr.flatMap(Object.values).flat() will do the job:

const arr =  [{JUNE: [{"iD": "67854", "event": " closed", "title": "test", "startDate": "2024-06-20", "endDate": "2024-07-25" } ] }, {MAY: [{"ID": "908765", "event": "closed", "title": "test", "startDate": "2024-05-21", "endDate": "2024-06-27" }, {ID: "12345", event: "open", title: "test123", startDate: "2024-05-21", endDate: "2024-06-27" } ] } ];

const result = arr.flatMap(Object.values).flat();

console.log(result)

answered Apr 1, 2024 at 22:41

Alexander Nenashev

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0stone0 · Accepted Answer · 2024-04-01 23:00:12Z

If you don't need the months, but just want to flatten it, flatMap and flat() it :

const arr =  [{JUNE: [{"iD": "67854", "event": " closed", "title": "test", "startDate": "2024-06-20", "endDate": "2024-07-25" } ] }, {MAY: [{"ID": "908765", "event": "closed", "title": "test", "startDate": "2024-05-21", "endDate": "2024-06-27" }, {ID: "12345", event: "open", title: "test123", startDate: "2024-05-21", endDate: "2024-06-27" } ] } ];

const res = arr.flatMap(c => Object.values(c).flat());

console.log(res)

If you want to add the month, thenreduce the array and flatMap each Object.keys with an deeper map for all the events.

const arr =  [{JUNE: [{"iD": "67854", "event": " closed", "title": "test", "startDate": "2024-06-20", "endDate": "2024-07-25" } ] }, {MAY: [{"ID": "908765", "event": "closed", "title": "test", "startDate": "2024-05-21", "endDate": "2024-06-27" }, {ID: "12345", event: "open", title: "test123", startDate: "2024-05-21", endDate: "2024-06-27" } ] } ];

const res = arr.reduce((p, c) => ([ ...p, 
    ...(Object.keys(c)
        .flatMap(month => c[month]
          .map(o => ({ ...o, month })) )) 
        ])
, []);

console.log(res)

Or as an one-liner":

const res = arr.reduce((p, c) => ([ ...p,...(Object.keys(c).flatMap(month => c[month].map(o => ({ ...o, month }))))]), []);

blex · Accepted Answer · 2024-04-01 21:54:30Z

One possible way to do it (not the most readable if you're not familiar with those) is to use reduce and concat like this:

const arr = [{JUNE:[{iD:"67854",event:" closed",title:"test",startDate:"2024-06-20",endDate:"2024-07-25"}]},{MAY:[{ID:"908765",event:"closed",title:"test",startDate:"2024-05-21",endDate:"2024-06-27"},{ID:"12345",event:"open",title:"test123",startDate:"2024-05-21",endDate:"2024-06-27"}]}];

const result = arr.reduce((acc, eventsByMonth) => acc.concat(
  ...Object.entries(eventsByMonth).reduce((acc, [month, events]) => acc.concat(
    ...events.map(event => ({ month, ...event }))
  ), [])
), []);

console.log(result);

reduce allows you to loop over an array and to aggregate data into an accumulator. In this case, the accumulator is your result array.

sam · Accepted Answer · 2024-04-01 22:07:29Z

You can use a reduce function to flatten your function:

const arr = [
    {
        JUNE: [
            {
                "iD": "67854",
                "event": " closed",
                "title": "test",
                "startDate": "2024-06-20",
                "endDate": "2024-07-25"
            }
        ]
    },
    {
        MAY: [
            {
                "ID": "908765",
                "event": "closed",
                "title": "test",
                "startDate": "2024-05-21",
                "endDate": "2024-06-27"
            },
            {
                ID: "12345",
                event: "open",
                title: "test123",
                startDate: "2024-05-21",
                endDate: "2024-06-27"
            }
        ]
    }
];

function flattenArray(array) {
    return array.reduce((acc, currentObj) => {
        Object.values(currentObj).forEach(nestedArray => {
            nestedArray.forEach(item => {
                // Not sure if it was a mistake or intended to have "iD" and "ID". 
// If not just skip this fix
                if (item.iD && !item.ID) {
                    item.ID = item.iD;
                    delete item.iD;
                }
                acc.push(item);
            });
        });
        return acc;
    }, []);
}

console.log(flattenArray(arr));

Ishan Majethia · Accepted Answer · 2024-04-01 21:54:27Z

Initialize a new array to hold the results.
Loop through each object in the original array.
For each object, access its property (which is an array).
Loop through each event in this array.
Create a new object from the event, adding the month property from the key of the object.
Push this new object to the results array.

const arr = [ /* your original array */ ];

const newArray = [];

arr.forEach(monthObject => {
  const month = Object.keys(monthObject)[0];
  monthObject[month].forEach(event => {
    const newEvent = { ...event,
      month: month.toUpperCase()
    };
    newArray.push(newEvent);
  });
});

console.log(newArray);

Based on the image you've provided, which shows the desired output format for your data transformation, it appears you want to convert an array of objects that represent events.

const events = [ /* your original array */ ];

const getMonthName = (dateString) => {
  const date = new Date(dateString);
  return date.toLocaleString('default', {
    month: 'long'
  }).toUpperCase();
}

const updatedEvents = events.map(event => {
  return {
    ...event,
    month: getMonthName(event.startDate)
  };
});

console.log(updatedEvents);

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