[Flutter] loop & list [ ] , map, where, reduce, every, any, for in

 

 Create a list with a loop in 1 line

You can put a for loop in [ ] to create a list.

List myList = [for(int i=0;i<10;i++) i];
print(myList); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

 Map

In many programming languages, a map is the name of a higher-order function that applies a given function to each element of a collection, e.g. a list or set, returning the results in a collection of the same type. It is often called apply-to-all when considered in functional form.

List myList = [1,2,3,4,5];
List myList2 = myList.map((item){
  return item * item;
}).toList();
print(myList2); // [1, 4, 9, 16, 25]

 Where

Returns a new lazy Iterable with all elements that satisfy the condition (predicate test). The matching elements have the same order in the returned iterable as in iterator.

List myList = ['apple','banana','cat','dog','egg','face','good'];
var result = myList.where((item){
  return item.contains('o');
});
print(result.toList());  //[dog, good]

 Reduce

Reduces a collection to a single value by iteratively combining elements of the collection using the provided function. The iterable must have at least one element. If it has only one element, that element is returned. Otherwise, this method starts with the first element from the iterator and then combines it with the remaining elements in iteration order.

1. accumulate
   
   

   List myList = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
   int result = myList.reduce((accumulator, currentElement){
    return accumulator + currentElement;
   });
   print(result);   // 55
   

2. find max
   
   

   List myList = [2,9,4,6,1,3,9,4,0,2];
   int result = myList.reduce((max, currentElement){
    return currentElement>max?currentElement:max;
   });
   print(result);   // 9
   

 Every

Checks whether every element of this iterable satisfies the test. Checks every element in iteration order, and returns false if any of them make test return false, otherwise returns true.

• every item < 5 ?
  
  

  List myList = [3,2,1,3,2,3];
  bool result = myList.every((item){
  return item < 5;
  });
  print(result); //true
  

 Any

Checks whether any element of this iterable satisfies the test. Checks every element in iteration order, and returns true if any of them make test return true, otherwise returns false.

• Is any number less than zero?
  
  

  List myList = [-1, 0, 1, 2, 3, 4, 5];
  bool result = myList.any((item){
  return item < 0;
  });
  print(result);   // true
  

 for…in

In Dart, the for...in loop takes an expression as an iterator and iterates through the elements one at a time in sequence.

List myList = [1, 2, 3, 4, 5];
for(int i in myList){
  print(i); //1 2 3 4 5
}