Full example

creator_function_full_example.dart

import 'dart:math';

var rng = new Random();

void main(List<String> args) {
  final quantity = 1000;
  final stopwatch = Stopwatch()..start();
  final products = createProducts(quantity);
  final users = createUsers(quantity);
  final usersIndexed = indexerListUser(users);

  goodCombinator(products, usersIndexed);
  // badCombinatorFunction(products, users);

  print(
      'Process for $quantity, executed in ${stopwatch.elapsed.inMilliseconds} milliseconds');

  stopwatch.stop();
}

goodCombinator(List<dynamic> products, List<dynamic> users) {
  final data = [];
  for (var i = 0; i < products.length; i++) {
    final user = users[products[i]['user']];
    data.add({
      "id": products[i]['id'],
      "name": products[i]['name'],
      "user": user,
    });
  }
  return data;
}

indexerListUser(List<dynamic> users) {
  final data = [];
  for (var i = 0; i < users.length; i++) {
    data.add({users[i]['id']: users[i]});
  }
  return data;
}

badCombinatorFunction(List<dynamic> products, List<dynamic> users) {
  final data = [];
  for (var i = 0; i < products.length; i++) {
    final user = users.firstWhere((u) => u['id'] == products[i]['user']);
    data.add({
      "id": products[i]['id'],
      "name": products[i]['name'],
      "user": user,
    });
  }
  return data;
}

createProducts(int quantity) {
  final data = [];
  for (var i = 0; i < quantity; i++) {
    data.add({"id": i, "name": "name $i", "user": rng.nextInt(quantity - 1)});
  }
  return data;
}

createUsers(int quantity) {
  final data = [];
  for (var i = 0; i < quantity; i++) {
    data.add({"id": i, "user": "User $i"});
  }
  return data;
}