How two sum multiple objects in a list matching a certain condition

user_16516595 0
Viewed 48

I'm struggling to understand how to sum multiple objects in a list together matching certain conditions

I have :

List<TruckFruit> = truckFruits;

class TruckFruit extends Equatable {
  final String fruitType;
  final int shape;
  final int availableCount;
  final int totalCount;

  TruckFruit({
    required this.fruitType,
    required this.shape,
    required this.availableCount,
    required this.totalCount,
  });

  @override
  List<Object?> get props => [
        shape,
        fruitType,
        availableCount,
        totalCount,
      ];
}

I'd like to sum multiple TruckFruit inside this truckFruits list which have equal fruitType String && equal shape int

such as from this list :

final List<TruckFruit> truckFruits = [
  TruckFruit(fruitType: 'Apple', shape: 4, availableCount: 1, totalCount: 10),
  TruckFruit(
      fruitType: 'Strawberry', shape: 4, availableCount: 2, totalCount: 6),
  TruckFruit(fruitType: 'Apple', shape: 4, availableCount: 8, totalCount: 30),
  TruckFruit(
      fruitType: 'Strawberry', shape: 2, availableCount: 5, totalCount: 8),
];

I'd like to get this list :


final List<TruckFruit> newTruckFruitsList = [
  TruckFruit(fruitType: 'Apple', shape: 4, availableCount: 9, totalCount: 40), // the availableCount & totalCount were summed from the two Apples with same shape
  TruckFruit(
      fruitType: 'Strawberry', shape: 4, availableCount: 2, totalCount: 6),
  TruckFruit(
      fruitType: 'Strawberry', shape: 2, availableCount: 5, totalCount: 8),
];
dart flutter
2 Answers

This could do it:

final List<TruckFruit> newTruckFruitsList = truckFruits.fold(<TruckFruit>[], (previousValue, element) {
  TruckFruit? match = previousValue.firstWhereOrNull(
      (e) => e.shape == element.shape && e.fruitType == element.fruitType);
  if (match != null) {
    return previousValue
      ..remove(match)
      ..add(TruckFruit(
          fruitType: element.fruitType,
          shape: element.shape,
          availableCount: element.availableCount + match.availableCount,
          totalCount: element.totalCount + match.totalCount));
  } else {
    return previousValue..add(element);
  }
});

You will need to

import 'package:collection/collection.dart';

to use firstWhereOrNull

user_15148610

create newTruckFruitsList by looping through truckFruits and adding TruckFruit objects with unique fruitTypes.
and double loop through newTruckFruitsList-truckFruits and add availableCount, totalCount if fruitType and shape matches.

user_143677150
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