How to group array of objects by date in swift?

Question

Need to group according to date. Response coming is in sorted format. Need to apply a filter on date to group. Response coming from backend:

[
    {
    "date": "date1"
    }, 
    {
    "date": "date1"
    },
    {
    "date": "date1"
    },
    {
    "date": "date2"
    },
    {
    "date": "date2"
    },
    {
    "date": "date3"
    }
]

Required:

[
    [
        "date": "2017-05-30T12:40:39.000Z",
        "message": [
            {
                "date_time": 2017-05-30T12: 40: 39.000Z
            }
        ]
    ],
    [
        "date": "2017-05-31T05:43:17.000Z",
        "message": [
            {
                "date_time": 2017-05-31T05: 43: 17.000Z
            },
            {
                "date_time": 2017-05-31T05: 44: 15.000Z
            },
            {
                "date_time": 2017-05-31T05: 44: 38.000Z
            }
        ]
    ]
]

I have checked multiple answers but wasn't able to find a good solution.

Answer 1

This is my solution to group by date(just day, month and year):

let groupDic = Dictionary(grouping: arr) { (pendingCamera) -> DateComponents in

    let date = Calendar.current.dateComponents([.day, .year, .month], from: (pendingCamera.date)!)

    return date
}

Answer 2

You can use an array extension.

extension Array {
  func sliced(by dateComponents: Set<Calendar.Component>, for key: KeyPath<Element, Date>) -> [Date: [Element]] {
    let initial: [Date: [Element]] = [:]
    let groupedByDateComponents = reduce(into: initial) { acc, cur in
      let components = Calendar.current.dateComponents(dateComponents, from: cur[keyPath: key])
      let date = Calendar.current.date(from: components)!
      let existing = acc[date] ?? []
      acc[date] = existing + [cur]
    }

    return groupedByDateComponents
  }
}

You can use it on any model property using the Swift 5 KeyPath

let grouped = models.sliced(by: [.year, .month, .day], for: \.createdAt)