Dart Convert Map to List & List to Map

In this post we are going to learn convert Map to List and List to Map in Dart/Flutter.

 

What is List in Dart?

Dart represents arrays in the form of List objects. A List is simply an ordered group of objects

List is classified in two ways

  • Fixed Length List
  • Growable List

 

What is Map?

The Map object is a simple key/value pair. Keys and values in a map may be of any type. A Map is a dynamic collection

Map can be classified as below

  • Using Map Literals
  • Using a Map constructor

 

Let's check

Suppose we have a class called User

 

class User {
  String name;
  int age;

  User(this.name, this.age);

  @override
  String toString() {
    return '{ ${this.name}, ${this.age} }';
  }
}

 

Now let's convert List<User> into Map and vice versa

 

Convert Map to List in Dart/Flutter

 

Let's initialize Map

Map user_map = {'User1': 23, 'User2': 27, 'User3': 25};

 

We will convert this Map to List<Customer> with Customer.name from a key and Customer.age from a value.
Before that, initialize an empty list first

var user_list = [];

 

Using Map forEach() method

Now we convert our Map to List above using forEach() method

 

user_map.forEach((k, v) => user_list.add(User(k, v)));
  print(user_list);

 

In the code above, we create a new User object from each key-value pair, then add the object to the user_list.

Output:

[{ User1, 23 }, { User2, 27 }, { User3, 25 }]

 

 

Using Iterable forEach() method

 

We can also convert a Dart Map to List using Iterable forEach() method instead.

user_map.entries.forEach((e) => user_list.add(User(e.key, e.value)));
print(user_list);

 

Output:

[{ User1, 23 }, { User2, 27 }, { User3, 25 }]

 

Using Iterable map() method

Another way to convert Map to a Dart List is to use Iterable map() method

 

user_list = map.entries.map((e) => User(e.key, e.value)).toList();
print(user_list);

 

Each entry item of Map’s entries will be mapped to a User object with entry.key as user.name and entry.value as user.age.


Then we convert the Iterable result to List using toList() method

 

Output:

[{ User1, 23 }, { User2, 27 }, { User3, 25 }]

 

 

Convert List to Map in Dart/Flutter

 

Now Let's create a List with User Info

 

List list = [];
list.add(User('User1', 23));
list.add(User('User2', 27));
list.add(User('User3', 25));

 

Using Map.fromIterable()

We convert List<User> into Map using fromIterable() constructor

 

var map1 = Map.fromIterable(list, key: (e) => e.name, value: (e) => e.age);
print(map1);

 

Using Iterable forEach() method

We can convert Dart List to Map in another way: forEach() method

 

var map = {};
list.forEach((user) => map[user.name] = user.age);
print(map);

 

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Flutter

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Author: RRTutors