Dart - How to merge two list of objects into singe list - flutter

Question

2> as you can see below i have two list of object and i want to merge into single it should compare list based on date
//here is the list 1
List<Object1> list1=[
Object1("date":"1","day_data":12),
Object1("date":"2","day_data":15),
]
//here is the list 2
List<Object2> list2=[
Object2("date":"1","night_data":56),
Object2("date":"3","night_data":80),
];
//expected output
List<Object3> expectedList=[
Object3("date":"1","day_data":12,"night_data":56),
Object3("date":"2","day_data":15,"night_data":null),
Object3("date":"3","day_data":null,"night_data":80),
];

Answer 1

The code below should do the trick. It uses a Map where the keys are, let's say, the Primary Key. And the values are the reduce from list1 and list2 (It even merges duplicated items by date from list1 and/or list2). At the end, I've added some asserts to actually test if it works.
Here's also the DartPad to run it online.
class Object1 {
final String date;
final int day_data;
const Object1({required this.date, required this.day_data});
}
class Object2 {
final String date;
final int night_data;
const Object2({required this.date, required this.night_data});
}
class Object3 {
final String date;
final int? day_data;
final int? night_data;
const Object3({required this.date, this.day_data, this.night_data});
}
List<Object3> merge(List<Object1> obj1List, List<Object2> obj2List) {
final map = <String, Object3>{};
obj1List.forEach((obj1) =>
map.update(
obj1.date,
(obj3) => Object3(date: obj3.date, day_data: obj1.day_data, night_data: obj3.night_data),
ifAbsent: () => Object3(date: obj1.date, day_data: obj1.day_data, night_data: null),
));
obj2List.forEach((obj2) =>
map.update(
obj2.date,
(obj3) => Object3(date: obj3.date, day_data: obj3.day_data, night_data: obj2.night_data),
ifAbsent: () => Object3(date: obj2.date, day_data: null, night_data: obj2.night_data),
));
return map.values.toList()
..sort((a, b) => a.date.compareTo(b.date));
}
void main() {
//here is the list 1
List<Object1> list1=[
Object1(date:"1",day_data:12),
Object1(date:"2",day_data:15),
];
//here is the list 2
List<Object2> list2=[
Object2(date:"1",night_data:56),
Object2(date:"3",night_data:80),
];
List<Object3> actualList = merge(list1, list2);
//expected output
List<Object3> expectedList=[
Object3(date:"1",day_data:12,night_data:56),
Object3(date:"2",day_data:15,night_data:null),
Object3(date:"3",day_data:null,night_data:80),
];
print('Checking size...');
assert(actualList.length == expectedList.length);
print('OK');
print('Checking items...');
actualList.asMap().forEach((i, actual) {
final expected = expectedList[i];
print(' Checking item $i...');
assert(actual.date == expected.date);
assert(actual.day_data == expected.day_data);
assert(actual.night_data == expected.night_data);
print(' OK');
});
print('OK');
}

Answer 2

You need to do manually with two loops and comparing dates.

Answer 3

Hey you can achieve by compering two list and get list like below -
void compareList(){
List<ObjectModel> list1=[
ObjectModel(date:"1",dayData:12),
ObjectModel(date:"2",dayData:15),
];
//here is the list 2
List<ObjectModel> list2=[
ObjectModel(date:"1",nightData:56),
ObjectModel(date:"3",nightData:80),
];
//expected output
List<ObjectModel> expectedList= [];
list1.forEach((element) {
ObjectModel innerObject = list2.firstWhere((ObjectModel innerElement) => element.date == innerElement.date, orElse: (){return ObjectModel();});
if(innerObject.date !=null){
expectedList.add(ObjectModel(date:element.date,dayData:element.dayData,nightData: innerObject.nightData));
}else{
expectedList.add(element);
}
});
list2.forEach((element) {
ObjectModel innerObject = list1.firstWhere((ObjectModel innerElement) => element.date == innerElement.date, orElse: (){return ObjectModel();});
if(innerObject.date ==null){
expectedList.add(element);
}
});
print(expectedList.length);
}
class ObjectModel{
String? date;
int? dayData;
int? nightData;
ObjectModel({ this.date, this.dayData, this.nightData});
}