Dart programs to iterate through a map:

A Map in Dart is used to hold key-value pairs. We can have any type of key or value. The key should be unique. We can’t have two equal keys for a dart map. But we can have multiple values with the same content.

You can iterate through the key-value pairs, or only through the keys or only through the values. We can use forEach and for-in loop for the iteration. In this post, I am listing down a couple of different ways to do that.

1. forEach to iterate key-value pairs of a dart map:

The forEach function takes one function as its parameter in dart. You can use two parameters in the function to get both key and value of a map:

main() {
  var numMap = Map();
  numMap["one"] = 1;
  numMap["two"] = 2;
  numMap["three"] = 3;
  numMap["four"] = 4;
  numMap["five"] = 5;

  numMap.forEach((k, v) => print("Key : $k, Value : $v"));
}

Here, k and v are the key and value of the element it is iterating. It will print all keys and values of numMap:

Key : one, Value : 1
Key : two, Value : 2
Key : three, Value : 3
Key : four, Value : 4
Key : five, Value : 5

Download this example on Github

2. for-in to iterate keys and values :

You can get the value of a dart map pair if you know the key associated with that value. We can use map[key] to get the value for the key in the map. The keys property of a Dart map returns all the keys of the map.

By using one for-in loop, we can iterate through the keys and for each key, we can get the value:

main() {
  var numMap = Map();
  numMap["one"] = 1;
  numMap["two"] = 2;
  numMap["three"] = 3;
  numMap["four"] = 4;
  numMap["five"] = 5;

  for (var k in numMap.keys) {
    print("Key : $k, value : ${numMap[k]}");
  }
}

The output is similar to the above example.

Download this example on Github

3. forEach to print key-values using keys :

By using the forEach loop, we can iterate only through the keys and for each key, we can print the value:

main() {
  var numMap = Map();
  numMap["one"] = 1;
  numMap["two"] = 2;
  numMap["three"] = 3;
  numMap["four"] = 4;
  numMap["five"] = 5;

  numMap.keys.forEach((k) => print("Key : $k, Value : ${numMap[k]}"));
}

We are iterating over the keys returned by the keys property of the map numMap.

Download this example on Github

4. Iterate through the values:

The values property of Dart map returns one iterable holding the map values. You can use one forEach or for-in to iterate through these values. Example using for in:

main() {
  var numMap = Map();
  numMap["one"] = 1;
  numMap["two"] = 2;
  numMap["three"] = 3;
  numMap["four"] = 4;
  numMap["five"] = 5;

  for (var v in numMap.values) {
    print(v);
  }
}

If you don’t need the keys, you can use this approach to iterate only through the values.

Download this example on Github

5. Using entries:

The Entry is a key-value pair that represents one entry in a map. We can get the key and value using entry.key and entry.value properties. The .entries property returns one iterable of the map entries. We can use one for in or forEach loop to iterate through these entries and get the key-value pairs.

The below example iterates over the entries to print the key-value pairs:

a. By using for…in:

main() {
  var numMap = Map();
  numMap["one"] = 1;
  numMap["two"] = 2;
  numMap["three"] = 3;
  numMap["four"] = 4;
  numMap["five"] = 5;

  for (MapEntry e in numMap.entries) {
    print("Key ${e.key}, Value ${e.value}");
  }
}

Download this example on Github

b. By using forEach:

main() {
  var numMap = Map();
  numMap["one"] = 1;
  numMap["two"] = 2;
  numMap["three"] = 3;
  numMap["four"] = 4;
  numMap["five"] = 5;

  numMap.entries.forEach((e) => print("Key ${e.key}, Value ${e.value}"));
}

Download this example on Github

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