如何从 List<Object> 中获取唯一对象及其编号的列表

Question

我的对象列表，例如

List<Product> products = [product1, product2, product1, product2, product1, product1]

如何从列表中获取带有编号的唯一对象列表？

import 'package:built_value/serializer.dart';
import 'package:built_value/built_value.dart';

part 'product.g.dart';

abstract class Product implements Built<Product, ProductBuilder>{
  int get id;
  String get title;
  String get image;
  double get price;
  int get volume;

  static Serializer<Product> get serializer => _$productSerializer;
  Product._();
  factory Product([updates(ProductBuilder b)]) = _$Product;
}

我想用对象获取其他列表：

class OrderPosition {
int id;
String title;
int count; // number of unique elements from list 'products'
}

例如：

List<OrderPosition> = [
OrderPosition(1, title1, 4),
OrderPosition(2, title2, 2)
]

Answer 1

class Product {
  Product(this.id); // for operator == to work properly
  final int id;     // make at least the id immutable

  String title;
  String image;
  double price;
  int volume;

  bool operator ==(Object other) => identical(this, other) || (other as Product).id == id;

  int get hashCode => id.hashCode;
}

var uniqueProducts = products.toSet().toList();
var result = <OrderPosition>[];
for(var i = 0; i < uniqueProducts.length; i++) {
  result.add(
    OrderPosition(i, 
                  uniqueProducts[i].title, 
                  products.where((e) => e == uniqueProducts[i]).length)));
}