Map iteration

Learn to iterate over Maps with for-in and forEach.

Iterating a Map

Several ways exist to walk a Map. The first is forEach: ages.forEach((k, v) => print('$k: $v'));. It yields the key and the value in order.

The second is for-in over entries: for (var e in ages.entries) { print(e.key); }. Each e is a MapEntry with .key and .value fields.

To walk only keys or values, use ages.keys or ages.values. A Map keeps the insertion order, so the iteration order is predictable.

entries yields each pair as a MapEntry with .key and .value fields. keys returns only the keys, values only the values.

For example for (var k in ages.keys) print(k); writes each key on a new line. for (var v in ages.values) print(v); writes the values.

When the order of work matters, entries is handier; if you only care about one side, keys or values is a shortcut.

Create a Map<String, int> with two people. Use forEach to print each pair as $key: $value.

Show example solution

void main() {
  var ages = <String, int>{};
  ages['Ayşe'] = 28;
  ages['Mert'] = 31;
  ages.forEach((k, v) => print('$k: $v'));
}

The for-in loop

void main() {
  var ages = <String, int>{'Ayşe': 28};
  for (var e in ages.____) {
    print(e.key);
  }
}

Show answer

void main() {
  var ages = <String, int>{'Ayşe': 28};
  for (var e in ages.entries) {
    print(e.key);
  }
}