Getting the Index Key of Map or List in Flutter/Dart by Value
Introduction
Flutter, a popular open-source mobile application development framework, allows developers to create seamless cross-platform apps. Dart, the language used to create Flutter apps, has a simple and efficient syntax. When working with data structures like maps and lists, sometimes we need to get the index (or key) of a specific value within these data structures. In this article, we will explore how to get the index key of a map or list array in Flutter/Dart by its value.
Getting the Index of List by Value in Flutter/Dart
To find the index of a list by its value in Flutter/Dart, you can use the `indexOf()` or `firstWhere()` methods available in Dart’s built-in List class.
Using `indexOf()`
The `indexOf()` method returns the index of the first occurrence of the specified element in the list.
“`dart
void main() {
List
String target = ‘banana’;
int index = fruits.indexOf(target);
print(index); // Output: 1
print(index); // Output: 3
}
“`
If the list does not contain the specified value, `indexOf()` returns -1.
Using `firstWhere()`
The `firstWhere()` method returns the first element that satisfies the provided test.
“`dart
void main() {
List
String target = ‘banana’;
int index = fruits.indexOf(fruits.firstWhere((element) => element == target));
print(index); // Output: 1
print(index); // Output: 3
}
“`
Getting the Index of Map by Value in Flutter/Dart
To find the index of a map by its value, you can use the `keys()` or `values()` method to retrieve the Map’s keys or values, respectively.
Using `keys()`
You can use `keys()` to get a Set of keys for the given Map.
“`dart
void main() {
Map
‘name’: ‘John Doe’,
‘age’: 30,
‘address’: {
‘street’: ‘123 Main St’,
‘city’: ‘New York’,
‘state’: ‘NY’,
},
};
String target = ‘John Doe’;
int index;
person.keys.forEach((key) {
if (person[key] == target) {
index = person.keys.indexOf(key);
print(index); // Output: 0
}
});
}
“`
Using `values()`
You can use `values()` to get a collection of Map values.
“`dart
void main() {
Map
‘name’: ‘John Doe’,
‘age’: 30,
‘address’: {
‘street’: ‘123 Main St’,
‘city’: ‘New York’,
‘state’: ‘NY’,
},
};
String target = ‘John Doe’;
int index;
person.values.forEach((value) {
if (value == target) {
index = person.keys.indexOf(person.keys.firstWhere((key) => person[key] == value));
print(index); // Output: 0
}
});
}
“`
Conclusion
In this article, we explored how to get the index key of a map or list array in Flutter/Dart by its value. The examples provided showcase how to use Flutter/Dart’s built-in `indexOf()` and `firstWhere()` methods for lists, as well as the `keys()` and `values()` methods for maps. By incorporating these methods into your Flutter/Dart development projects, you can efficiently search and index your data structures.
Frequently Asked Questions (FAQs)
Q: Can I use `indexOf()` and `firstWhere()` methods with null or empty list?
A: Yes, `indexOf()` and `firstWhere()` methods will return `-1` for null or empty lists.
Q: What happens if there are multiple occurrences of the target value in the list?
A: `indexOf()` and `firstWhere()` methods will return the index of the first occurrence.
Q: How to get the index of a map by its nested value?
A: Use the `keys()` or `values()` method and search through the nested data structure by value.
Q: Can I use these methods with other data structures like `Set` or `LinkedHashMap`?
A: Yes, you can use these methods with `Set` and `LinkedHashMap`, but make sure to understand their respective implementation.
Q: What’s the time complexity of these methods?
A: The time complexity of `indexOf()` for arrays is O(n), while `firstWhere()` is O(n) as well. The `keys()` and `values()` methods for maps also have a time complexity of O(n).
