How to Set a Default Value for a Key in a Map in Dart - Step by Step Examples

How to Set a Default Value for a Key in a Map in Dart ?

Answer

To set a default value for a key in a map in Dart, you can use the putIfAbsent method.

✐ Examples

1 Setting a Default Value Using putIfAbsent Method

We can set a default value for a key in a map in Dart using the putIfAbsent method, which inserts a key-value pair if the key does not already exist in the map.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the putIfAbsent method to set a default value for a key. The putIfAbsent method takes the key and a function that returns the default value to be inserted if the key is not already present in the map.
We print the updated map to the console using the print function.

Dart Program

void main() {
    // Declare and initialize a map
    Map<String, int> myMap = {
        'one': 1,
        'two': 2,
        'three': 3
    };

    // Set a default value using putIfAbsent method
    myMap.putIfAbsent('four', () => 4);

    // Print the updated map
    print(myMap);
}

Output

{one: 1, two: 2, three: 3, four: 4}

2 Setting a Default Value Conditionally Using putIfAbsent Method

We can set a default value for a key in a map in Dart using the putIfAbsent method, which inserts a key-value pair if the key does not already exist in the map, based on a condition.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the putIfAbsent method to set a default value for a key based on a condition. The putIfAbsent method takes the key and a function that returns the default value to be inserted if the key is not already present in the map.
We print the updated map to the console using the print function.

Dart Program

void main() {
    // Declare and initialize a map
    Map<String, int> myMap = {
        'one': 1,
        'two': 2,
        'three': 3
    };

    // Set a default value conditionally using putIfAbsent method
    myMap.putIfAbsent('four', () => myMap['four'] ?? 4);

    // Print the updated map
    print(myMap);
}

Output

{one: 1, two: 2, three: 3, four: 4}

3 Setting Multiple Default Values Using putIfAbsent Method

We can set multiple default values for keys in a map in Dart using the putIfAbsent method, which inserts key-value pairs if the keys do not already exist in the map.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the putIfAbsent method to set multiple default values for keys. The putIfAbsent method takes the key and a function that returns the default value to be inserted if the key is not already present in the map.
We print the updated map to the console using the print function.

Dart Program

void main() {
    // Declare and initialize a map
    Map<String, int> myMap = {
        'one': 1,
        'two': 2,
        'three': 3
    };

    // Set multiple default values using putIfAbsent method
    myMap.putIfAbsent('four', () => 4);
    myMap.putIfAbsent('five', () => 5);

    // Print the updated map
    print(myMap);
}

Output

{one: 1, two: 2, three: 3, four: 4, five: 5}

Summary

In this tutorial, we learned How to Set a Default Value for a Key in a Map in Dart language with well detailed examples.

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How to Set a Default Value for a Key in a Map in Dart - Step by Step Examples