I'm returning a flat List from my server with objects that contain a createdAt. I want to iterate through this list and find the most recent one created, sorted by a specific key, kind

for example, this is the data I'm receiving:

final list = [
  {id: '1a' kind: 'MOOD' createdAt: 2021-12-08 19:22:11.000Z},
  {id: '1b' kind: 'MOOD' createdAt: 2021-12-08 19:15:11.000Z},
  {id: '1c' kind: 'PRESSURE' createdAt: 2021-12-08 18:22:11.000Z},
  {id: '1d' kind: 'MOOD' createdAt: 2021-12-07 18:22:11.000Z},
  {id: '1e' kind: 'WEIGHT' createdAt: 2021-12-07 17:21:11.000Z},
]

I want to be able to get the most recent createdAt, by the item's kind, so, for example, I want to get MOOD's most recent entry, it would be

{id: '1a' kind: 'MOOD' createdAt: 2021-12-08 19:22:11.000Z}

Similarly, I want to get WEIGHT's most recent entry, which would return

  {id: '1e' kind: 'WEIGHT' createdAt: 2021-12-07 17:21:11.000Z},

I've tried using firstWhere, but I'm unsure how to find the most recent date of the list, so I'm a bit lost there. I also have access to collection if a method there is applicable.

CodePudding user response：

Your objects match the next type:

class Obj {
  final String id;
  final String kind;
  final String createdAt;
  
  Obj(this.id, this.kind, this.createdAt);
  
  String toString() {
    return 'Obj{id: $id, kind: $kind, createdAt: $createdAt}';
  }
}

So you can use the next method to get the most recent one:

Obj findEarliestByKind(List<Obj> list, String kind) {
  final elems = list.where((Obj item) => item.kind == kind).toList();
  elems.sort((a, b) => DateTime.parse(b.createdAt).compareTo(DateTime.parse(a.createdAt)));
  return elems[0];
}

Some additional notes:

1. It's better to pass type as an Enum
2. It's needed to handle parsing and empty list exceptions

CodePudding user response：

Try to use DateTime.parse to convert string to DateTime object. Then you can get milliseconds from epoch. For example:

  Map<String, dynamic> getElement(List list, String kind) {
  list.where((element) => element['kind'] == kind).toList().sort((a, b) {
    return DateTime.parse(b['createdAt']!).millisecondsSinceEpoch -
        DateTime.parse(a['createdAt']!).millisecondsSinceEpoch;
  });

  return list.first;
}