how to group data In flutter-CodePudding

I have just made a demo to clear what I want in my app

Like, I have a class model name Transaction and have some data like below

List<Transaction> transactionlist=[
  Transaction(category: 'Food', amount: 100.00),
  Transaction(category: 'Food', amount: 200.00),
  Transaction(category: 'Shopping', amount: 1000.00),
  Transaction(category: 'Shopping', amount: 2000.00),
  Transaction(category: 'Food', amount: 300.00),
  Transaction(category: 'Provision', amount: 500.00),
];

Now I want to show all category with its expense total , and therefor I have created a widget class...

class ShowCategoryStatus extends StatelessWidget {

  final List<Transaction> transactionlist;
  ShowCategoryStatus({required this.transactionlist});

  List<Map<String,Object>> get amoutbycategory{

//what should I code here to get following list
    /*this getter should return like following way
    [
  {
    'Category':'Food','total':600
  },
  {
    'Category':'Shopping','total':3000.00
  },
  {
    'Category':'Provision','total':500
  }

]


*/


  }

CodePudding user response：

You can so this:

    List<Transaction> result = [];
    for (var e in transactionlist) {
      var x = result.where((element) => element.category == e.category);
      if (x.isEmpty) {
        result.add(e);
      } else {
        var newTransaction = Transaction(
            category: e.category, amount: x.first.amount   e.amount);

        result[result.indexOf(x.first)] = newTransaction;
      }
    }

Short Version: you can use collection package, and try this:

Map<String, List<Transaction>> grouped =
        groupBy(transactionlist, (value) => value.category);

List<Transaction> result = grouped.entries
        .map((e) => Transaction(
            category: e.key,
            amount: e.value.fold(0, (total, ele) => total   ele.amount)))
        .toList();

now if you print the result you will see what you want:

for (var element in result) {
  print("result =${element.category} ${element.amount}"); 
// result =Food 600.0
// result =Shopping 3000.0
// result =Provision 500.0
}

CodePudding user response：

You could use a combination of groupBy, map and fold:

  List<Transaction> transactionlist = [
    Transaction(category: 'Food', amount: 100.00),
    Transaction(category: 'Food', amount: 200.00),
    Transaction(category: 'Shopping', amount: 1000.00),
    Transaction(category: 'Shopping', amount: 2000.00),
    Transaction(category: 'Food', amount: 300.00),
    Transaction(category: 'Provision', amount: 500.00),
  ];

  Map<String, List<Transaction>> catGroup =
      groupBy(transactionlist, (val) => val.category);

  Map<String, double> amountMap = catGroup.map((key, value) =>
      MapEntry(key, value.fold(0, (total, ele) => total   ele.amount)));

  print(amountMap);

The groupBy is used to group all Transactions by their category. map is used to convert between Maps, and finally fold is use to sum up all the amounts of a certain category. You could probably also use reduce to sum the amounts here since the iterable should never be empty.

CodePudding user response：

hope you are fine,

Simple and slightly hard coded answer: you need to loop over list and check for category to sum amount and then return result.

void main() {
 List<Transaction> transactions=[
 Transaction(category: 'Food', amount: 100.0),
 Transaction(category: 'Food', amount: 200.0),
 Transaction(category: 'Shopping', amount: 1000.0),
 Transaction(category: 'Shopping', amount: 2000.0),
 Transaction(category: 'Food', amount: 300.0),
 Transaction(category: 'Provision', amount: 500.0),
 ];

 Transaction.amountByCategory(transactions);
 print(Transaction.amountByCategory(transactions)
 );
}

class Transaction{
 String? category;
 double? amount;
 Transaction({this.category, this.amount});

 static List<Map<String, dynamic>> amountByCategory(List<Transaction> 
 transactions) {
   var foodAmount = 0.0;
   var shoppingAmount = 0.0;
   var provisionAmount = 0.0;

   transactions.map((transaction) {
    switch(transaction.category){
      case "Food":
      foodAmount  = transaction.amount!.toDouble();
      break;
     
      case "Shopping":
      shoppingAmount  = transaction.amount!.toDouble();
      break;
     
      case "Provision":
      provisionAmount  = transaction.amount!.toDouble();
      break;
   }}).toList();

return [
  {
    "Category": "Food",
    "total": foodAmount,
  },
   {
    "Category": "Shopping",
    "total": shoppingAmount,
  },
   {
    "Category": "Provision",
    "total": provisionAmount,
   },
  ];
 },
}

code link -> https://dartpad.dev/?

hope I could help, have a nice day :)

CodePudding user response：

Best to way to do this, is put your logic out side of UI.

You can use extension which are very powerful & useful for this kind of cases.

extension TransactionUtils on List<Transaction> {
  List<Map<String, dynamic>> get categories {
    // create a map for result
    Map<String, double> totalAmounts = {};
    forEach((transaction) {
      totalAmounts.update(
        transaction.category,
        (oldAmount) => oldAmount   transaction.amount,
        ifAbsent: () => transaction.amount,
      );
    });

    //? your data is ready
    // {'Food': 600.0, 'Shopping': 3000.0, 'Provision': 500.0}
    print(totalAmounts);

    //? if you want list of map
    // [
    //   {"category": "Food", "total": 600.0},
    //   {"category": "Shopping", "total": 3000.0},
    //   {"category": "Provision", "total": 500.0}
    // ];
    return totalAmounts.entries
        .map((mapEntry) => {'category': mapEntry.key, 'total': mapEntry.value})
        .toList();
  }
}

& in your UI you can use following way:

void main() {
  final myData = transactionList.categories;
}

You can find detailed explanation about extension on Vandad's blog.