Dart Maps

In this chapter, we will learn about dart maps data types and the properties and methods of map that are available in dart.

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Dart Map

In dart, a map denote a collection of data in key/value pairs. The key and value can be of any data type. For example,

var person = {'name': 'Phil', 'age': 25, 'isMale': true};

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Declaring Map

We can create a map data type in two ways.

1. Using map literal

2. Using map constructor

Using map literal

We can create map data type by enclosing the value in curly braces and separating each pair by comma. For example,

void main() {
var person = {'name': 'Phil', 'age': 25, 'isMale': true};
print(person);
}

Output

{name: Phil, age: 25, isMale: true}

Using map Constructor

Another way to create map data is by passing the new keyword to the Map constructor. For example,

void main() { 
   var person = new Map(); 
   person['name'] = 'Phil'; 
   person['age'] = 25;
   person['isMale'] = true;
   print(person); 
}

Output

{name: Phil, age: 25, isMale: true}

Note: In map data types, keys must be unique.

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Dart Map Properties

Maps data types provide various properties. Some of them are:

Properties	Description
length	Returns the number of key/value pairs in the map
values	Returns an iterable object representing values
keys	Returns an iterable object representing keys
isEmpty	Returns true if the map is an empty map
isNotEmpty	Returns false if the map is an empty Map

Map Properties Examples

void main() {
var person = {'name': 'Phil', 'age': 25, 'isMale': true};
print(person);

print(person.length);
print(person.isEmpty);
print(person.isNotEmpty);
print(person.keys);
print(person.values);
}

Output

{name: Phil, age: 25, isMale: true}
3
false
true
(name, age, isMale)
(Phil, 25, true)

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Dart Map Methods

Maps data type also has multiple methods available. Some of them are:

Methods	Description
clear()	Removes all pairs from the map
addAll()	Adds all key-value pairs of other to this map
remove()	Removes key and its associated value

Map Method Examples

void main() {
var person = {'name': 'Phil', 'age': 25, 'isMale': true};
print(person);

person.addAll({'address': 'New York', 'email': '[email protected]'});
print('After adding: ${person}');

person.remove('age');
print('After removing: ${person}');

person.clear();
print('After clearing: ${person}');
}

Output

{name: Phil, age: 25, isMale: true}
After adding: {name: Phil, age: 25, isMale: true, address: New York, email: [email protected]}
After removing: {name: Phil, isMale: true, address: New York, email: [email protected]}
After clearing: {}