How can I return an array of values from an array of grouped objects in js?

Question

I have an array of subscriptions group by the type (basic,medium ...) `

[
  [
    "Basic",
    [
      { "id": 2, "name": "Basic", "started_at": "2022-01-24", "count": 4 },
      { "id": 2, "name": "Basic", "started_at": "2022-03-16", "count": 2 },
      { "id": 2, "name": "Basic", "started_at": "2022-05-16", "count": 1 }
    ]
  ],
  [
    "Medium",
    [
      { "id": 3, "name": "Medium", "started_at": "2022-02-21", "count": 1 },
      { "id": 3, "name": "Medium", "started_at": "2022-05-28", "count": 1 }
    ]
  ],
  [
    "Premium",
    [{ "id": 4, "name": "Premium", "started_at": "2022-04-21", "count": 1 }]
  ],
  [
    "Master",
    [
      { "id": 7, "name": "Master", "started_at": "2022-07-28", "count": 1 },
      { "id": 7, "name": "Master", "started_at": "2022-08-02", "count": 1 }
    ]
  ],
  [
    "Jedi",
    [{ "id": 6, "name": "Jedi", "started_at": "2022-09-28", "count": 1 }]
  ]
]

`

What I want to do is return an array containing objects foreach sub with the following data(get the count value by month): `

[
  {
    label: "Basic",
    data: [4, 0, 2, 0, 1,0],
  },
  {
    label: "Medium",
    data: [0, 1, 0, 0, 1,0],
  },
  ...
]

`

The data field should contain the count field foreach subscription corresponding to the month. For example for with count 4 in January and count 2 in March it will return [4,0,1] with 0 for February.

How can I achieve that ?

I did this but it's returning only the existing month values so there is no way to know which month that value is for.

subscriptions.map((item) => {
            return {
                label: item[0],
                data: item[1].map((value, index) => {
                    return value.count;
                }),
            };
        })

Can there be multiple started_at dates on the same date/month for the same name? Can started_at also be 2022 and also be for 2023 in the one group? — Nick Parsons
– Nick Parsons, Commented Dec 28, 2022 at 10:40
Do you want for the whole year or only just the first six months? Master has data for July and August. — adiga
– adiga, Commented Dec 28, 2022 at 10:41
@NickParsons In one group yes we can have multiple objects with differents started_at — Abdelhk
– Abdelhk, Commented Dec 28, 2022 at 13:02
@adiga I want to print the data depending on the entries for the hole year so for master the data field should look like this [0,0,0,0,0,0,1,1,0,0,0,0] — Abdelhk
– Abdelhk, Commented Dec 28, 2022 at 13:05

adiga · Accepted Answer · 2022-12-28 11:10:39Z

2

You could reduce the array and create a mapper object which maps each plan with month specifc count. Something like this:

{
  "Basic": {
    "1": 4,
    "3": 2,
    "5": 1
  },
  "Medium": {
    "2": 1,
    "5": 1
  },
  ...
}

Then loop through the entries of the object and create objects with plan as label and an array of length: 12 and get the data for that specific month using the index

const input=[["Basic",[{id:2,name:"Basic",started_at:"2022-01-24",count:4},{id:2,name:"Basic",started_at:"2022-03-16",count:2},{id:2,name:"Basic",started_at:"2022-05-16",count:1}]],["Medium",[{id:3,name:"Medium",started_at:"2022-02-21",count:1},{id:3,name:"Medium",started_at:"2022-05-28",count:1}]],["Premium",[{id:4,name:"Premium",started_at:"2022-04-21",count:1}]],["Master",[{id:7,name:"Master",started_at:"2022-07-28",count:1},{id:7,name:"Master",started_at:"2022-08-02",count:1}]],["Jedi",[{id:6,name:"Jedi",started_at:"2022-09-28",count:1}]]];

const mapper = input.reduce((acc, [plan, subscriptions]) => {
   acc[plan] ??= {}

  for(const { started_at, count } of subscriptions)
    acc[plan][+started_at.slice(5,7)] = count
  
  return acc;
}, {})

const output = 
    Object.entries(mapper)
           .map( ([label, subData]) => ({ 
                label, 
                data: Array.from({ length: 12 }, (_, i) => subData[i+1] ?? 0) 
              }) )
              
console.log(output)

Note:

This assumes that the data is for a single year only. If it can be across years you'd have to create another level of nesting:
```
{
  "Basic": {
    "2022": {
      "1": 3
    }
  }
}
```
started_at.slice(5,7) is used to get the month number. If the dates are not in the ISO 8601 format, you can use new Date(started_at).getMonth() + 1 to get the month part.

edited Dec 28, 2022 at 11:10

answered Dec 28, 2022 at 10:54

adiga

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2 Comments

Soorya J Over a year ago

I have a doubt, I tried to answer by having a for each inside map(), it is not working and you have used reduce() any specific reason why reduce() and not a for loop ?

adiga Over a year ago

@SooryaJ you can use a for loop or a forEach with a const mapper = {} declared outside. reduce is just a functional way of doing it. map is not appropriate here.

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