I have an array in the flutter
final list = [1, 2, 3, 4, 5];
I want to loop through the array to calculate the sum of all the items in the array,how i can?
Try the following:
final list = [1, 2, 3, 4, 5];
final result = list.reduce((sum, element){
return sum + element;
});
This could do it
final sum = list.fold<int>(0, (previousValue, number) => previousValue + number);
Related
I have a list that contains some values I want to calculate the sum of every 4 items in this list and then I have to put it in a list.
for example:
list 1=[1,2,3,4,5,6,7,8]
output= [10,26]
You can play with snippet.
final List<int> list = [1, 2, 3, 4, 5, 6, 7, 8, 9];
final List<List<int>> subLists = [];
for (int i = 0; i < list.length / 4; i++) {
final start = i * 4;
final end = i * 4 + 4;
subLists
.add(list.sublist(start, end > list.length ? list.length : end));
}
print(subLists); //[[1, 2, 3, 4], [5, 6, 7, 8], [9]]
final results = subLists
.map((l) => l.reduce((value, element) => value + element))
.toList();
print(results); //[10, 26, 9]
You can use this custom-made extension method to sum every n in a `List``, just add it inside your file outside your classes :
extension SumEveryExtension on List<num> {
List<num> sumEvery(int n) {
num nSumTracker = 0;
List<num> result = [];
for (int index = 0; index < length; index += 1) {
nSumTracker += this[index];
print("current" + nSumTracker.toString());
if ((index +1) % (n ) == 0 && index != 0) {
result.add(nSumTracker);
nSumTracker = 0;
}
}
return result;
}
}
And use it in your code like this:
List<int> list = [1, 2, 3, 4, 5, 6, 7, 8];
print(list.sumEvery(4)); // [10, 26]
You can also customize the n from the method to sum for any other n.
Store data in a 1-dimensional List and add() it to a 2-dimensional List.
After add(), .clear() the one-dimensional List.
However, since List refers to an address, clear() loses the address, so the 2D array becomes an empty List. Is there a way to keep the values in a 2D List even after clearing?
List<int> num = [1, 2, 3];
List<List<int> num2 = [];
num2.add(num);
num.clear();
You could use List.from() to perform shallow copy
List<int> num = [1, 2, 3];
List<List<int>> num2 = [];
num2.add(List.from(num));
print(num2); //[[1, 2, 3]]
num.clear();
print(num2); //[[1, 2, 3]]
use trick with toList() method
void main() {
List<int> num1 = [1, 2, 3];
List<List<int>> num2 = [[0,2]] ;
num2.add(num1.toList());
num1.clear();
print(num2); // [[0, 2], [1, 2, 3]]
print(num1); // []
}
You should add list as anonymous list
List<int> num = [1, 2, 3];
List<List<int>> num2 = [];
// add as anonymous list
num2.add(num.toList());
num.clear();
print(num2.length); // 1
print(num.length); // 0
for (var element in num2) {
print(element.length); // 3
}
I want to check if items in array existed and add new values from another array without overwriting element after reloading. I created such code:
//take from that array
List<int> list = [2, 3, 5];
// add to this array and check if this array already has the same element or not
List<int> newValueInt = [2, 6, 7];
list.forEach((item) {
if(!list.contains(item)){
newValueInt.add(item);
print(newValueInt);
}
});
and it shows me that print:
[2, 6, 7, 3]
[2, 6, 7, 3, 5]
List<int> list = [2, 3, 5];
// add to this array and check if this array already has the same element or not
List<int> newValueInt = [2, 6, 7];
List<int> temp = [];
for (var item in list) {
if(!newValueInt.contains(item)){
temp.add(item);
}
}
List<int> result = newValueInt + temp;
print(result); //---> [2, 6, 7, 3, 5]
if(!list.contains(item)){
to
if(! newValueInt.contains(item)){
How do we do math to each item in a list (add numbers from variable and multiply final value) and return another List?
Something like this:
var list = [1, 2, 3, 4, 5];
print(list); // Prints [1, 2, 3, 4, 5]
var list2 = list.map((i) => i * 2 + 5 /* math here*/).toList();
print(list2); // Prints [7, 9, 11, 13, 15]
So I'm working on an app in Flutter, and long story short: I have 2 'filter options' which create 2 seperate lists. Now what I want is to use those 2 Lists and find the items which are present in BOTH lists and add that item to a third List.
Example:
List<int> first_list = [1, 2, 3, 4, 5];
List<int> second_list = [1, 2, 8, 9];
Result: [1, 2]
I know I could potentially loop through 1 list and then check with 'contains()' if the item is present in the other list. But it could be that 1 (or both) lists are empty and then my third list will be empty as I simply will never loop to add a duplicate item to the third list
Something like this?
void main() {
List<int> first_list = [1, 2, 3, 4, 5];
List<int> second_list = [1, 2, 8, 9];
final shared = [...first_list.where(second_list.contains)];
print(shared); // [1, 2]
}
What you need is intersection between two collections. Most likely it makes sense not to use lists, but rather sets of items.
I would solve this like that:
void main() {
List<int> first_list = [1, 2, 3, 4, 5];
List<int> second_list = [1, 2, 8, 9];
final shared = first_list.toSet().intersection(second_list.toSet());
print(shared);
}
If you can work with sets, not with lists it would be even simpler:
void main() {
Set<int> first_list = {1, 2, 3, 4, 5};
Set<int> second_list = {1, 2, 8, 9};
final shared = first_list.intersection(second_list);
print(shared);
}
You can use intersection
List<int> firstList = [1, 2, 3, 4, 5];
List<int> secondList = [1, 2, 8, 9];
final firsToSet = firstList.toSet();
final secondToSet = secondList.toSet();
final res = firsToSet.intersection(secondToSet);
print(res);