Flutter & Dart: fold() method examples

Some common use cases of the fold() method in Dart (and Flutter as well).

Calculating the Sum of a List

What this example does is simply find the sum of a given numeric list:

import 'package:flutter/foundation.dart';

void main() {
  final List<int> myList = [1, 3, 5, 8, 7, 2, 11];
  final int result = myList.fold(0, (sum, element) => sum + element);

  if (kDebugMode) {
    print(result);
  }
}

Output:

37

Finding the biggest number (the maximum) in a List

The fold() method gives us an elegant way to spot the max number of a numeric list:

import 'package:flutter/foundation.dart';

void main() {
  final myList = [1, 3, 5, 8, 7, 2, 11];
  final int result = myList.fold(myList.first, (max, element) {
    if (max < element) max = element;
    return max;
  });

  if (kDebugMode) {
    print(result);
  }
}

Output:

11

Find the smallest number (the minimum) in a List

This example does the opposite thing compared to the previous one: get the min from a list of numbers.

import 'package:flutter/foundation.dart';

void main() {
  final myList = [10, 3, 5, 8, 7, 2, 11];
  final int result = myList.fold(myList.first, (min, element) {
    if (min > element) min = element;
    return min;
  });

  if (kDebugMode) {
    print(result);
  }
}

Output:

2

Wrap Up

We’ve gone over some examples of using the fold() method in Dart programs. If you’d like to explore more about Dart and Flutter development, take a look at the following articles:

• Dart & Flutter: 2 Ways to Count Words in a String
• Dart: Calculate the Sum of all Values in a Map
• Sorting Lists in Dart and Flutter (5 Examples)
• 2 ways to remove duplicate items from a list in Dart
• Flutter & Dart: Get File Name and Extension from Path/URL
• 4 ways to convert Double to Int in Flutter & Dart

You can also check out our Flutter category page, or Dart category page for the latest tutorials and examples.