Map

Learn key-value collections with Map<K,V>.

Map<K,V>

Map<K,V> stores key-value pairs. Each key is unique; one key maps to one value. K is the key type and V is the value type.

Create a Map with var scores = <String, int>{'Alex': 90, 'Mia': 85};. Keys are String, values are int. To add a new pair write scores['Bob'] = 78;.

Access a value with scores['Alex']. The length gives the pair count. A Map is ideal for name-age, product-price and similar mappings.

Map operations

To add a pair write map['key'] = value. If the key exists the value is updated. Access a value again with map['key'].

Example: var s = <String, int>{'Alex': 90}; s['Bob'] = 78; print(s);. Output: {Alex: 90, Bob: 78}. s.length gives 2.

A Map provides fast lookup. A value is reached by key in average O(1) time. This is far more efficient than lists for large data sets.

Exercise Create a score table

Create a score table with <String, int>{'Alex': 90, 'Mia': 85}. Add a new pair with scores['Bob'] = 78. Print the Map first, then the length.

Show example solution

void main() {
  var scores = <String, int>{'Alex': 90, 'Mia': 85};
  scores['Bob'] = 78;
  print(scores);
  print(scores.length);
}

Test yourself

Match the Map parts

<String, int>

Key and value type
{'Alex': 90}

Key-value pair
scores['Bob'] = 78

Add a new pair
length

Pair count
What happens if you assign two values to the same Map key?
```
var m = <String, int>{};
m['a'] = 1;
m['a'] = 2;
```
- Two 'a' keys appear
- It throws an error
- The second value overwrites the first
- The values are summed
Show answer

The second value overwrites the first — assigning to the same key overwrites the previous value.

Add a pair to the Map

var scores = <String, int>{'Alex': 90};
____['Bob'] = 78;

Show answer

var scores = <String, int>{'Alex': 90};
scores['Bob'] = 78;

Next lesson: Queue

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies