Dart List min/max value

Question

How do you get the min and max values of a List in Dart.

[1, 2, 3, 4, 5].min //returns 1
[1, 2, 3, 4, 5].max //returns 5

I'm sure I could a) write a short function or b) copy then sort the list and select the last value,

but I'm looking to see if there is a more native solution if there is any.

Answer 1

Assuming the list is not empty you can use Iterable.reduce :

import 'dart:math';

main(){
  print([1,2,8,6].reduce(max)); // 8
  print([1,2,8,6].reduce(min)); // 1
}

Answer 2

If you don't want to import dart: math and still wants to use reduce:

main() {
  List list = [2,8,1,6]; // List should not be empty.
  print(list.reduce((curr, next) => curr > next? curr: next)); // 8 --> Max
  print(list.reduce((curr, next) => curr < next? curr: next)); // 1 --> Min
}

Answer 3

You can now achieve this with an extension as of Dart 2.6:

import 'dart:math';

void main() {
  [1, 2, 3, 4, 5].min; // returns 1
  [1, 2, 3, 4, 5].max; // returns 5
}

extension FancyIterable on Iterable<int> {
  int get max => reduce(math.max);

  int get min => reduce(math.min);
}

Answer 4

An example to get Min/Max value using reduce based on condition for a list of Map objects

Map studentA = {
  'Name': 'John',
  'Marks': 85
};

Map studentB = {
  'Name': 'Peter',
  'Marks': 70
};

List<Map> students = [studentA, studentB];

// Get student having maximum mark from the list

Map studentWithMaxMarks = students.reduce((a, b) {
    if (a["Marks"] > b["Marks"])
        return a;
    else
        return b;
});


// Get student having minimum mark from the list (one liner)

Map studentWithMinMarks = students.reduce((a, b) => a["Marks"] < b["Marks"] ? a : b);

Another example to get Min/Max value using reduce based on condition for a list of class objects

class Student {
    final String Name;
    final int Marks;

    Student(this.Name, this.Marks);
}

final studentA = Student('John', 85);
final studentB = Student('Peter', 70);

List<Student> students = [studentA, studentB];

// Get student having minimum marks from the list

Student studentWithMinMarks = students.reduce((a, b) => a.Marks < b.Marks ? a : b);

Answer 5

For empty lists: This will return 0 if list is empty, the max value otherwise.

  List<int> x = [ ];  
  print(x.isEmpty ? 0 : x.reduce(max)); //prints 0

  List<int> x = [1,32,5];  
  print(x.isEmpty ? 0 : x.reduce(max)); //prints 32

Answer 6

Using fold method with dart:math library

Example:

// Main function 
void main() { 
  // Creating a geek list 
  var geekList = [121, 12, 33, 14, 3]; 
    
  // Declaring and assigning 
  // the largestGeekValue and smallestGeekValue 
  // Finding the smallest and 
  // largest value in the list 
  var smallestGeekValue = geekList.fold(geekList[0],min); 
  var largestGeekValue = geekList.fold(geekList[0],max); 
  
  // Printing the values 
  print("Smallest value in the list : $smallestGeekValue"); 
  print("Largest value in the list : $largestGeekValue"); 
}

Output:

Smallest value in the list : 3
Largest value in the list : 121

Answer from : https://www.geeksforgeeks.org/dart-finding-minimum-and-maximum-value-in-a-list/

Answer 7

If your list is empty, reduce will throw an error.

You can use fold instead of reduce.

// nan compare to any number will return false
final initialValue = number.nan;
// max
values.fold(initialValue, (previousValue, element) => element.value > previousValue ? element.value : previousValue);
// min
values.fold(initialValue, (previousValue, element) => element.value < previousValue ? element.value : previousValue);

It can also use to calculate sum.

final initialValue = 0;
values.fold(initialValue, (previousValue, element) => element.value + previousValue);

Although fold is not cleaner than reduce for getting min/max, it is still a powerful method to do more flexible actions.