How to Get the Size (Number of Key-Value Pairs) of a Map in Dart

How to Get the Size (Number of Key-Value Pairs) of a Map in Dart ?

Answer

To get the size (number of key-value pairs) of a map in Dart, you can use the length property. This property returns the number of elements in the map.

✐ Examples

1 Getting the Size of a Map Using length Property

We can get the size of a map in Dart using the length property, which provides the number of key-value pairs 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 length property to get the number of key-value pairs in the map.
We store the size in a variable named mapSize.
We print the size to the console using the print function to verify the number of key-value pairs in the map.

Dart Program

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

    // Get the size of the map
    int mapSize = myMap.length;

    // Print the size
    print('Size of the map: $mapSize');
}

Output

Size of the map: 3

2 Getting the Size of an Empty Map

We can also get the size of an empty map in Dart using the length property, which returns 0 when the map is empty.

For example,

We start by declaring an empty map named emptyMap with string keys and integer values.
We use the length property to get the number of key-value pairs in the empty map.
We store the size in a variable named emptyMapSize.
We print the size to the console using the print function to verify that the map is empty.

Dart Program

void main() {
    // Declare an empty map
    Map<String, int> emptyMap = {};

    // Get the size of the empty map
    int emptyMapSize = emptyMap.length;

    // Print the size
    print('Size of the empty map: $emptyMapSize');
}

Output

Size of the empty map: 0

3 Getting the Size of a Map After Adding Elements

We can get the size of a map in Dart after adding elements using the length property, which provides the updated number of key-value pairs in the map.

For example,

We start by declaring an empty map named dynamicMap with string keys and integer values.
We add some key-value pairs to the map using the map's index notation.
We use the length property to get the number of key-value pairs in the map after adding elements.
We store the size in a variable named dynamicMapSize.
We print the size to the console using the print function to verify the updated number of key-value pairs in the map.

Dart Program

void main() {
    // Declare an empty map
    Map<String, int> dynamicMap = {};

    // Add elements to the map
    dynamicMap['one'] = 1;
    dynamicMap['two'] = 2;
    dynamicMap['three'] = 3;

    // Get the size of the map after adding elements
    int dynamicMapSize = dynamicMap.length;

    // Print the size
    print('Size of the map after adding elements: $dynamicMapSize');
}

Output

Size of the map after adding elements: 3

Summary

In this tutorial, we learned How to Get the Size (Number of Key-Value Pairs) of a Map in Dart language with well detailed examples.

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How to Get the Size (Number of Key-Value Pairs) of a Map in Dart