Dart: How to create new list Using Existing List?

Question

i am new to flutter . I am trying to create new list from below list

 var itemlist1=[
          {"p_id": "a101", "model": "M-Plaz","price": 2500},
          {"p_id": "a101", "model": "Z-Plaz","price": 3500},
          {"p_id": "a102", "model": "M-Neo", "price": 1560},
          {"p_id": "a102", "model": "N-Neo1","price": 3600}];

Output list should be like below

var newlist=[{"Subitems":[
    {
        "p_id":"a101",
        "items": [
            {"p_id": "a101", "model": "M-Plaz","price": 2500},
          {"p_id": "a101", "model": "Z-Plaz","price": 3500}     
        ]},{
        "p_id": "a102",
        "items": [
           {"p_id": "a102", "model": "M-Neo", "price": 1560},
          {"p_id": "a102", "model": "N-Neo1","price": 3600}
        ]},
    ]
}];

please i need help..

nagendra nag · Accepted Answer · 2022-02-28 05:46:00Z

1

The below code gives you the required output.

var itemlist1 = [
      {"p_id": "a101", "model": "M-Plaz", "price": 2500},
      {"p_id": "a101", "model": "Z-Plaz", "price": 3500},
      {"p_id": "a102", "model": "M-Neo", "price": 1560},
      {"p_id": "a102", "model": "N-Neo1", "price": 3600}
    ];

    var newlist = groupBy(itemlist1, (Map obj) => obj['p_id']);

    var requiredOutput = [
      {"Subitems": []}
    ];
    newlist.forEach((k, v) => {
          requiredOutput[0]["Subitems"]!.add({"p_id": k, "items": v})
        });

    print(requiredOutput);

Note: Add import "package:collection/collection.dart"; line in imports.

answered Feb 28, 2022 at 5:46

nagendra nag

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2 Comments

nagendra nag Over a year ago

@srikantha nayak no need of thanks. if the solution is work for you then reply as it's working otherwise reply as it's not working or something else. then the person who is answering your question may get clarity about his answer.

shrikantha nayak Over a year ago

got it sir.. im new here. so you good people are helping me.. by now i will reply revery answers . thank you for your kindness.

Siddharth Mehra · Accepted Answer · 2022-02-28 05:17:21Z

0

You can do this by:

newlist.addAll([
  {'Subitems': itemlist1}
]);

print(newlist.toString());

edited Feb 28, 2022 at 5:17

answered Feb 28, 2022 at 5:07

Siddharth Mehra

1,9171 gold badge18 silver badges38 bronze badges

2 Comments

Siddharth Mehra Over a year ago

okay, let me update.

Siddharth Mehra Over a year ago

now try, it should work.

DeePanShu · Accepted Answer · 2022-02-28 06:25:28Z

Try this code snippet:

 var itemlist1=[
          {"p_id": "a101", "model": "M-Plaz","price": 2500},
          {"p_id": "a101", "model": "Z-Plaz","price": 3500},
          {"p_id": "a102", "model": "M-Neo", "price": 1560},
          {"p_id": "a102", "model": "N-Neo1","price": 3600}];

 // list for subItems
  var subItems = [];
  itemlist1.forEach((item){
     
     // check for subitem for p_id already exists or not
     List items =  subItems.where((i)=>
        i['p_id'] == (item)['p_id']
      ).toList();
    
      if(items.length > 0 ){
        (items[0] as Map<String,dynamic>)['items'].add(item);
      }else {
          Map newMap = Map<String,dynamic>();
          newMap.putIfAbsent('p_id', () => (item)['p_id'].toString());
          List newList = [item];
          newMap.putIfAbsent('items', () => newList);
          subItems.add(newMap);
      } 
    });
    
 
   var output = [
      {"Subitems": subItems}
    ];

  print(output);

Thierry · Accepted Answer · 2022-02-28 13:29:45Z

0

I would recommend you not to work directly on a Map<String, dynamic> you get from Json. You could rather define a Model for your Products.

class ProductModel {
  final String pId;
  final String model;
  final double price;
  
  ProductModel({
    required this.pId,
    required this.model,
    required this.price
  });
  
  ProductModel.fromJson(Map<String, dynamic> json):
    pId = json['p_id'] as String,
    model = json['model'] as String,
    price = json['price'] as double;
  
  Map<String, dynamic> toJson() => {
    'p_id': pId,
    'model': model,
    'price': price
  };
}

Note: Have a look at the json_serializable & freezed packages too.

Then, grouping your Products by id gets easier:

void main() {
  final List<ProductModel> list =[
    {"p_id": "a101", "model": "M-Plaz","price": 2500},
    {"p_id": "a101", "model": "Z-Plaz","price": 3500},
    {"p_id": "a102", "model": "M-Neo", "price": 1560},
    {"p_id": "a102", "model": "N-Neo1","price": 3600},
  ].map((item) => ProductModel.fromJson(item)).toList();
  final Map<String, List<ProductModel>> processed = list.fold({}, (pMap, productModel) => {
    ...pMap,
    productModel.pId: [...(pMap[productModel.pId] ?? []), productModel]
  });
  print(jsonEncode(processed));
}

Console log:

{"a101":[{"p_id":"a101","model":"M-Plaz","price":2500},{"p_id":"a101","model":"Z-Plaz","price":3500}],"a102":[{"p_id":"a102","model":"M-Neo","price":1560},{"p_id":"a102","model":"N-Neo1","price":3600}]}

Remark

With your Output format, in order to get the models for p_id 'a101', you will have to:

final a101Models = newlist[0]['Subitems']?.singleWhere((product) => product['p_id'] == 'a101')['items']

With my recommended solution, it gets easier:

List<ProductModel> a101Models = processed['a101'];
```

edited Feb 28, 2022 at 13:29

answered Feb 28, 2022 at 6:20

Thierry

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2 Comments

shrikantha nayak Over a year ago

from this code im not getting correct result.

Thierry Over a year ago

Yes, with this code, you have to change your Output format. This might make the rest of your application easier. Check my last update on this solution.

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