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Working with Maps

This guide explores practical map operations through real-world examples including phone directories and user profiles.

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Basic Map Operations: Phone Directory

Let’s create a phone directory using a map: 
Map<String, String> telefonos = {
  'Juan': '8764521111',
  'María': '8764521222'
};

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Searching for Contacts

Check if a contact exists before accessing it: 
if (telefonos.containsKey('Juan')) {
  print('Teléfono de Juan: ${telefonos['Juan']}');
} else {
  print('Contacto No Existe!!!!');
}
Always use containsKey() to verify a key exists before accessing it to avoid null values.

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Adding Contacts Dynamically

You can add new entries to a map after creation: 
import 'dart:io';

String nombre = '';
for (var i = 0; i < 3; i++) {
  print('Nombre del Contacto:');
  nombre = stdin.readLineSync()!;
  print('Número de Telefono de $nombre:');
  telefonos[nombre] = stdin.readLineSync()!;
}

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Iterating Through Maps

Use the forEach() method to iterate through all key-value pairs: 
print('\nRecorrido de un Diccionario:');
telefonos.forEach((clave, valor){
  print('$clave: $valor');
});
Output: 
Recorrido de un Diccionario:
Juan: 8764521111
María: 8764521222
Pedro: 8764523333
The forEach() method takes a function with two parameters: the key and the value.

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Maps with Dynamic Values

Maps can store different types of values using the dynamic type: 
Map<String, dynamic> usuario = {
  'nombre': 'Roberto',
  'edad': 20,
  'activo': true,
  'calificacion': 8.5
};

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Accessing Different Types

print(usuario['nombre']); // Roberto (String)
print(usuario['edad']);  // 20 (int)
print(usuario['activo']); // true (bool)
print(usuario['calificacion']); // 8.5 (double)
When using dynamic, Dart can’t check types at compile time. Be careful when accessing values to avoid runtime errors.

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Iterating Dynamic Maps

Use forEach() with dynamic maps just like regular maps: 
print('\nImprimir con ForEach');
usuario.forEach((llave, valor){
  print('$llave: $valor');
});
Output: 
Imprimir con ForEach
nombre: Roberto
edad: 20
activo: true
calificacion: 8.5

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Complete Examples

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Example 1: Phone Directory

import 'dart:io';

void main() {
  Map<String, String> telefonos = {
    'Juan': '8764521111',
    'María': '8764521222'
  };

  // Buscar
  if (telefonos.containsKey('Juan')) {
    print('Teléfono de Juan: ${telefonos['Juan']}');
  } else 
    print('Contacto No Existe!!!!');

  //Agregar Datos al Diccionario
  String nombre = '';
  for (var i = 0; i < 3; i++) {
    print('Nombre del Contacto:');
    nombre = stdin.readLineSync()!;
    print('Número de Telefono de $nombre:');
    telefonos[nombre] = stdin.readLineSync()!;
  }

  // Iterar
  print('\nRecorrido de un Diccionario:');
  telefonos.forEach((clave, valor){
    print('$clave: $valor');
  });
  print('');
  
}

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Example 2: User Profile

void main() {
  Map<String, dynamic> usuario = {
    'nombre': 'Roberto',
    'edad': 20,
    'activo': true,
    'calificacion': 8.5
  };

  print(usuario['nombre']); // Roberto
  print(usuario['edad']);  // 20
  print(usuario['activo']); // true
  print(usuario['calificacion']); // 8.5

  print('\nImprimir con ForEach');
  usuario.forEach((llave, valor){
    print('$llave: $valor');
  });
}

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Common Map Operations

OperationMethodDescriptionExample
Add/Updatemap[key] = valueAdds or updates entrytelefonos['Ana'] = '123'
SearchcontainsKey(key)Check if key existstelefonos.containsKey('Juan')
Accessmap[key]Get value by keytelefonos['Juan']
IterateforEach()Loop through entriesmap.forEach((k, v) => ...)
Removeremove(key)Delete entrytelefonos.remove('Juan')

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Iteration Methods Comparison

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Method 1: forEach()

Best for simple iteration: 
map.forEach((key, value) {
  print('$key: $value');
});

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Method 2: for-in with keys

When you need more control: 
for (var key in map.keys) {
  print('$key: ${map[key]}');
}

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Method 3: entries

When you need both key and value as objects: 
for (var entry in map.entries) {
  print('${entry.key}: ${entry.value}');
}

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Use Cases for Different Map Types

String to String

Phone directories, translations, configuration settings

String to int

Ages, scores, quantities, IDs

String to dynamic

User profiles, JSON-like data, flexible configurations

int to String

Error codes to messages, ID to name mappings

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Type Safety Considerations

Map<String, int> ages = {'Alice': 25, 'Bob': 30};
int aliceAge = ages['Alice']!; // Type safe
Use strongly typed maps when all values are the same type for better type safety and IDE support.

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Dynamic Maps (Use with Caution)

Map<String, dynamic> user = {'name': 'Alice', 'age': 25};
String name = user['name'] as String; // Need type casting
int age = user['age'] as int;
With dynamic maps, you lose compile-time type checking and need to cast values. Use only when necessary (e.g., JSON parsing).

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Practical Patterns

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Pattern 1: Safe Access with Default Value

String phone = telefonos['Unknown'] ?? 'No phone available';

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Pattern 2: Conditional Update

if (!telefonos.containsKey('Pedro')) {
  telefonos['Pedro'] = '8764525555';
}

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Pattern 3: Bulk Operations

Map<String, String> newContacts = {
  'Ana': '111111',
  'Luis': '222222'
};
telefonos.addAll(newContacts);

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Pattern 4: Filter and Transform

// Get only active users
Map<String, dynamic> activeUsers = Map.fromEntries(
  usuarios.entries.where((entry) => entry.value['activo'] == true)
);

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Best Practices

  1. Use appropriate types: Choose Map<String, int> over Map<String, dynamic> when possible
  2. Check before access: Always use containsKey() or null-aware operators
  3. Use forEach() for iteration: It’s more concise and readable than manual loops
  4. Meaningful keys: Use descriptive key names that represent the data
  5. Handle null values: Maps return null for non-existent keys, so handle this appropriately
Remember: Map keys must be unique, but values can repeat. If you add an existing key, it will update the value, not create a duplicate.

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