Flutter Dart Convert Map to List & List to Map

Last updated Apr 03, 2022

In this post we are going to cover about What is List and Map and How to convert list to map and map to list with dart programming.
In any programming language array is the common data type to manage the collection of data. In dart we will use List to manage group of data. List is an group of ordered list data. To use List we will use dart:core package

In dart List could be divided in two parts

Fixed Length List
Growable List

Fixed Length List : A fixed length list can't change its length at runtime. We will create Fixed Length list like below

var list = new List(SIZE_OF_LIST);

Simple Fixed Length List example

void main() {
   var lst = new List(3);
   lst[0] = 1;
   lst[1] = 2;
   lst[2] = 3;
   lst[3] = 12;
   print(lst);
}

This will print below output

[1, 2, 3,12]

Growable List : Its a Growable list where length can change at runtime.

var list = new List(growable:true);
void main() {
var intList = [12,11,123];
print(intList);
}

What is Map in dart?

When we want to store the data with aperticular names then we will use Maps. Map is an collection data typw which will store the data in the form of Key/Value pair. Map can change at runtime, it can grow or shrink on the run time.
we can declare map in two ways

Using Map Literals
Using a Map constructor

Delcare Map using Map Listerals

var mapName = { key1:value1, key2:value2 ,.... }

Simple Map example using Map Literals

void main() {
var details = {'name':'Rahim','age':'25'};
print(details);
}

Till now we discussed what is Map and List in dart, let learn how to convert Map to List in dart

class Student {
String name;
int marks;

Student(this.name, this.marks);

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

Let create a Simple Map object which will contains info about the Students

var student=Student(name:"Student1",marks:230);
Map studentMap={"student1":Student};

Now let create an Empty list object

var studentList = [];

Convert Map to list using Map forEach() method

studentMap.forEach((k, v) => studentList.add(v);
print(studentList);

Here we generated list from map using key,values and will print below out put

void main() {

var student=Student(name:"Student1",marks:230);
Map studentMap={"student1":Student};

print(studentMap);

var studentList = [];
   studentMap.forEach((k, v) {

     studentList.add(v);
   } );
print(studentList);
}

class Student {
String? name;
int? marks;

Student({this.name, this.marks});

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

Convert List to Map in Dart/Flutter

Now Let's create a List with Student Info

List list = [];
list.add(Student(name:'Student1', marks:231));
list.add(Student(name:'Student2', marks:432));
list.add(Student(name:'Student3', marks:123));

Convert List to Map 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.marks);
print(map);

Output:

{Student1: 231, Student2: 432, Student3: 123}

void main() {
List list = [];
list.add(Student(name:'Student1', marks:231));
list.add(Student(name:'Student2', marks:432));
list.add(Student(name:'Student3', marks:123));

print(list);

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

class Student {
String? name;
int? marks;

Student({this.name, this.marks});

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

Read dart list tutorial

Compare list and maps using DeepCollectionEquality collection class

Conclusion: In this Dart tutorial we covered how to convert list to map and map to list in different ways

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