Dart - Map

void main(List<String> args) {

  Map<int, String> m1 = {};
  m1[1] = 'red';
  m1[2] = 'green';
  m1[3] = 'blue';
  print(m1.values.last);

  // Map은 중복 키를 허용하지 않기 때문에
  // 내용 교체하려면 삭제 후 추가를 해야 한다.
  // 그래서 .update 메서드를 제공한다.

  m1.update(3, (value) => 'black', ifAbsent:() => 'newColor');
  m1.update(4, (value) => 'black', ifAbsent:() => 'newColor');
  print(m1);
}

// 결과
blue
{1: red, 2: green, 3: black, 4: newColor}

 

void main(List<String> args) {
  Map<String, double> expenses = {'sun': 2000.0, 'mon': 1000.0, 'tue': 3000.0};

  print("All keys of Map: ${expenses.keys}");
  print("All values of Map: ${expenses.values}");
  print("Is Map empty: ${expenses.isEmpty}");
  print("Is Map not empty: ${expenses.isNotEmpty}");
  print("Length of Map is: ${expenses.length}");

  print("==============================");

  // Looping Over Element Of Map
  for (var ex in expenses.entries) {
    print("Key: ${ex.key}, Value: ${ex.value}");
  }

  // Looping In Map Using For Each
  expenses.forEach((key, value) => expenses.update(key, (value) => value + 1));
  print("add plus one to Map's value is: $expenses");
}

// 결과
All keys of Map: (sun, mon, tue)
All values of Map: (2000.0, 1000.0, 3000.0)
Is Map empty: false
Is Map not empty: true
Length of Map is: 3
==============================
Key: sun, Value: 2000.0
Key: mon, Value: 1000.0
Key: tue, Value: 3000.0
add plus one to Map's value is: {sun: 2001.0, mon: 1001.0, tue: 3001.0}

 

void main(List<String> args) {
  List vals = ['apply', 'ban', 'appoint', 'work'];
  List meetCondition = vals
      .where((item) => (item.toString().startsWith('a') && item.length < 6))
      .toList();
  print(meetCondition);

  print("==============================");

  // Student's exam marks
  //
  // format: Student ID, Gender, marks1, marks2

  Map studentsMarks = {
    'Jane': {
      0002: ['female', 80, 90],
    },
    'John': {
      0010: ['male', 75, 95],
    },
    'Ken': {
      0109: ['male', 70, 55]
    }
  };

  // print(studentsMarks['Jane'][0002]);

  // total marks of male students
  int totalMarksOfMaleStudents = 0;

  for (var sEntry in studentsMarks.entries) {
    for (var mEntry in sEntry.value.entries) {
      if (mEntry.value[0] == 'male') {
        totalMarksOfMaleStudents += mEntry.value[1] as int;
        totalMarksOfMaleStudents += mEntry.value[2] as int;
      }
    }
  }

  print(totalMarksOfMaleStudents);
}

// 결과
[apply]
==============================
295

 

void main(List<String> args) {
  bool condition = true;
  try {
    assert(condition != true, "condition is false.");
  } catch (e) {
    print(e);
  }

  print("==============================");

  // How to Find Index Value Of List
  var footballPlayers = ['Ronaldo', 'Messi', 'Neymar', 'Hazard'];
  footballPlayers
      .asMap()
      .forEach((index, item) => print("index: $index, item: $item"));

  print("==============================");

  // Print Unicode Value of Each Character of String
  String name = "John";
  for (var codePoint in name.runes) {
    print("Unicode of ${String.fromCharCode(codePoint)} is $codePoint.");
  }
}

// 결과
'file:///C:/Users/SKTelecom/Documents/Dart_code/dart_application_1/bin/dart_application89.dart': Failed assertion: line 4 pos 12: 'condition != true': condition is false.
==============================
index: 0, item: Ronaldo
index: 1, item: Messi
index: 2, item: Neymar
index: 3, item: Hazard
==============================
Unicode of J is 74.
Unicode of o is 111.
Unicode of h is 104.
Unicode of n is 110.

 

void main(List<String> args) {
  // Creating a map
  var intMap01 = {"one": 1, "two": 2, "three": 3};
  print(intMap01);

  var intMap02 = <String, int>{"one": 1, "two": 2, "three": 3};
  print(intMap02);

  Map<String, int> intMap03 = {"one": 1, "two": 2, "three": 3};
  print(intMap03);

  Map intMap04 = <String, int>{"one": 1, "two": 2, "three": 3};
  print(intMap04);

  // Accessing elements from a map
  print(intMap04['one']);

  // Adding elements to a map
  Map<String, int> numbers = {'one': 1, 'two': 2, 'three': 3};
  numbers['four'] = 4;
  print(numbers);

  var totalValue = 0;
  numbers.forEach((key, value) {
    totalValue += value;
  });

  print(
      "total of using reduce: ${numbers.values.reduce((value, element) => value + element)}");

  print("total of using foreach: $totalValue");

  // Checking for the existence of keys or values
  print("Is key: one exist? ${numbers.containsKey('one')}");
  print("Is value: 1 exist? ${numbers.containsValue(1)}");
}

// 결과
{one: 1, two: 2, three: 3}
{one: 1, two: 2, three: 3}
{one: 1, two: 2, three: 3}
{one: 1, two: 2, three: 3}
1
{one: 1, two: 2, three: 3, four: 4}
total of using reduce: 10
total of using foreach: 10
Is key: one exist? true
Is value: 1 exist? true

 

/*
You can use the entries property of a map. 
To iterate over elements of the map, 
you can iterate over the map.entries. 
Each MapEntry object has two properties including key and value. 
*/

void main(List<String> args) {
  var numbers = {"one": 1, "two": 2, "three": 3};
  for (var num in numbers.entries) {
    print("${num.key}: ${num.value}");
  }
}

// 결과
one: 1
two: 2
three: 3

 

// Dart map()
//
// map() is one of transformer.

void main(List<String> args) {
  var nums = [1, 2, 3];
  var newNums = getNewNums(nums);
  print(newNums);

  print("");

  var anotherNums = (nums.map((e) => e + 1)).toList();
  print(anotherNums);
}

List<int> getNewNums(List<int> nums) {
  List<int> newNums = [];
  for (var n in nums) {
    newNums.add(n + 1);
  }
  return newNums;
}

// 결과
[2, 3, 4]

[2, 3, 4]

 

void main(List<String> args) {
  // An iterable is a collection of items that can be accessed sequentially.
  // List and sets are iterable, but maps aren't.

  Map<String, dynamic> person = {'name': 'John', 'age': 36, 'height': 1.84};

  for (var entry in person.entries) {
    print("${entry.key}:, ${entry.value}");
  }
}

// 결과
name:, John
age:, 36
height:, 1.84

 

void main(List<String> args) {
  final ratings = [4.0, 4.5, 3.5];
  final restaurant = {
    'name': 'Pizza Mario',
    'cuisine': 'Italian',
    ...{
      if (ratings.length >= 3) 'ratings': ratings,
      'isPopular': true,
    }
  };

  print(restaurant);
}

// 결과
{name: Pizza Mario, cuisine: Italian, ratings: [4.0, 4.5, 3.5], isPopular: true}

 

void main(List<String> args) {
  var restaurants = [
    {
      'name': 'Pizza Mario',
      'cuisine': 'Italian',
      'ratings': [5.0, 3.5, 4.5],
    },
    {
      'name': 'Chez Anne',
      'cuisine': 'French',
      'ratings': [5.0, 4.5, 4.0],
    },
    {
      'name': 'Navaratna',
      'cuisine': 'Indian',
      'ratings': [4.0, 4.5, 4.0],
    },
  ];

  for (var rest in restaurants) {
    double sum = 0;
    final ratings = rest['ratings'] as List<double>;
    for (double r in ratings) {
      sum += r;
    }
    rest['avgRatings'] = sum / rest.length;
  }

  print(restaurants);
}

// 결과
[{name: Pizza Mario, cuisine: Italian, ratings: [5.0, 3.5, 4.5], avgRatings: 4.333333333333333}, {name: Chez Anne, cuisine: French, ratings: [5.0, 4.5, 4.0], avgRatings: 4.5}, {name: Navaratna, cuisine: Indian, ratings: [4.0, 4.5, 4.0], avgRatings: 4.166666666666667}]

 

void main(List<String> args) {
  const pizzaPrices = {'margherita': 5.5, 'pepperoni': 7.5, 'vegetarian': 6.5};

  const order = ['margherita', 'pepperoni', 'pineapple'];

  double sum = 0;
  for (String o in order) {
    if (pizzaPrices.containsKey(o)) {
      sum += pizzaPrices[o] as double;
    }
  }

  print(sum);
}

// 결과
13.0

 

void main(List<String> args) {
  var user = {
    'username': 'peter',
    'password': 'peter123',
    'role': 'admin',
    'staffNr': 9911,
  };

  Map<String, dynamic> user2 = {};

  var password = user['password'];
  // print(password.length); // 이 경우 password의 타입이 object이므로 length 메소드를 호출할 수 없음

  var password2 = user['password'] as String;
  print(password2.length); // 그러나 String 형변환을 하면 length 메소드 호출 가능

  // accessing values that do not exist
  var ipAddress = user['ipAddress'];
  print(ipAddress); // null

  var ipAddress2 = user['ipAddress'];
  if (ipAddress2 == null) {
    print('The value is empty');
  } else {
    print(ipAddress2);
  }

  print('');

  for (var entry in user.entries) {
    print('${entry.key} : ${entry.value}');
  }
}

/*
maps or dictionaries in other languages
collection of key-value pairs

username: peter
password: peter123
role: admin
staffNr: 9911
*/

// 결과
8
null
The value is empty
username : peter
password : peter123
role : admin
staffNr : 9911

 

import 'dart:math' as Math;

void main(List<String> args) {
  var map1 = {
    'student': 'Peter',
    'mark': 40,
  };

  var map2 = {
    'student': 'Paul',
    'mark': 76,
  };

  var map3 = {
    'student': 'James',
    'mark': 89,
  };

  var marks = [map1, map2, map3];
  double sumMarks = 0.0;
  String lowestStudent = marks[0]['student'] as String;
  int lowestMark = marks[0]['mark'] as int;

  String highestStudent = marks[0]['student'] as String;
  int highestMark = marks[0]['mark'] as int;

  for (var mark in marks) {
    sumMarks += mark['mark'] as int;

    if (mark['mark'] as int < lowestMark) {
      lowestMark = mark['mark'] as int;
      lowestStudent = mark['student'] as String;
    }

    if (mark['mark'] as int > highestMark) {
      highestMark = mark['mark'] as int;
      highestStudent = mark['student'] as String;
    }
  }

  print('The student with the highest mark is $highestStudent, $highestMark');
  print('The student with the lowest mark is $lowestStudent, $lowestMark');

  print(
      'The avg of the marks is ${(sumMarks / marks.length).toStringAsFixed(2)}');
}

// 결과
The student with the highest mark is James, 89
The student with the lowest mark is Peter, 40
The avg of the marks is 68.33