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3-Lists & Sets

Content

Lists

Lists, as they name say, can list a lot of values, this values will be determinated by the type of data which is defined after the list definition, and it has to be between <>.

List<TypeOfData> list1 = [];

Replacement

You can replace values inside of a list, like other programming languages

List<String> lista = ["Jhon", "Marston"];
// We're going to replace "Jhon" by "Arthur" and "Marston" by "Morgan"
lista[0] = "Arthur";
lista[1] = "Morgan";

Functions

In a list, you can add, delete, modify and read all data inside of a list

Add Elements

You will be able to add element by element (individually) or a bunch of values. See the example below

List<String> list1 = ["Hi!"];
list1.add("I'm"); // An individual element

List<String> listToAdd = ["Alan", ":D"];
list1.addAll(listToAdd);

Also, you can add lists manually when you create a new list. You can do it using ... before the name if the list to add. See the sample below:

List<int> list1 = [1,2,3];
List<int> list2 = [4,5,6];

List<int> completeList = [...list1, ...list2, 7, 8]; // Using "..."

Insert Method

This method allows you to insert an element in an specific index inside of the list:

// First Parameter is the index desired to insert the element, that is the second parameter
completeList.insert(1, 2)

Remove

By element

You can remove values from a list using the method remove:

// A bunch of code here :D
list.remove("bannana");
// ...

This method returns true if something inside has been removed, or false otherwise.

bool removed = list.remove("bannana2");

By index

As its name says, This method will remove the element of the index specified as parameter

list.removeAt(2);

This method return the element in that index:

int numberInTheList = list.removeAt(2);

Remove all

To clear all list, you have tu use:

list.clear();

Sets

Definition

What Are sets in Flutter?

In Flutter (usingDart), sets are unordered collections of unique elements. Unlike lists, they do not allow duplicate values and do not maintain the order in which elements were added. Sets are useful for ensuring uniqueness, removing duplicates from a list, and performing mathematical set operations like union and intersection

Example

// Set<DataType> = [data]
Set<String> name = {"Alan", "dunkel"};

Functions

Add elements

As a "set" list, it is not allowed duplicating elements, Flutter directly will skip this attemp to add something existing in the list. For example, following the previous example (using name list), "Alan" already exists, so if I try to add "Alan" twice, you can see what will happen below

name.add("Alan");
print(name);

Output

{"Alan", "dunkel"}
Note

It is importante to say that if there is a word begining with Capital letter (for example, Jhon) and you add the same word (jhon) but begining with lower case, Those will be able to coexist

name.add("alan");

Output will be:

{"Alan", "dunkel", "alan"}

Remove Elements

To remove elements, .remove() is the functions that does this. Taking the last case as example:

name.remove("alan");
print(name);

Output:

{"Alan", "dunkel"}

Clear "set" list

name.clear()

Remove a bunch of elements

Set<String> name2 = {"Alan", "dunkel"};
name.removeAll(name2); // This removes all elements inside of 'name2'

Get length

int nameAmount = name.length;

Knowing if something exists

In dart, in "set" lists section, you will find contains() method, thata returns bool proving if something exists or not:

name.contains("Alan"); // this returns true
name.contains("alan"); // this returns false

Convert a List to set

It is useful if you want to delete elements repeated, because when you convert a list to "set" list, elements repeated are automatically eliminated

List<String> list = ["One", "two", "One"];
Set<String> newList = Set.from(list);

Map lists

In other programming languages, to this type of lists are known like "dictionaries". You have a key, and each key has a value

Map<String, String> users = {
	"Admin": "Alan",
	"User": "Alfonso",
	"Customer": "Job"
};

Also key may have different data type from its value:

Map<String, float> accounts = {
	"alan223hfr": 200.0,
	"alfonxxsw": 344.34,
	"jonsjob": 0.0
};

Set new Values

If you want to change the amount of "alan", you have to access to the key of that value:

accounts["alan223hfr"] = 100.0;

Functions

Add a bunch of elements

As you can in lists or "set" lists, you may add more elements:

Map<String, float> accountsAdded = {"alan22": 230.0, "josue": 1200.0};
accounts.addAll(accountsAdded);

Add one single element

Different from lists or "set" lists, here you only have to write a new key and its value:

accounts["alan333": 50.50]; // This does not exist in accounts, so it will be added inmediatly

Accessing to keys and its values

Proving if there is something existing in a map list

If you want to know the existence of an specific element:

accounts.containsKey("key") // this will verify if "key" is inside of accounts as key value

accounts.containsValue("Value") // this will verify if "value" is inside of accounts as value

Other common functions

Bucles for applied in lists

We have two ways to pass through a list:

List<int> lista = [1,2,3,4];
for(var i = 0; i < lista.length; i++) {
	print("${lista[i]}")
}

or a kind of foreach function

for (int number in lista) {
	print("$number");
}

Bucles for applied in maps

Map<int,int> listb = {1 => 100, 2 => 200, 3 => 300, 4 => 400};

for (var element in listb.entries) {
	print("${element.key} its value is ${element.value}");
}

Bucles foreach applied in lists and maps

Lists and sets

Foreach is a better way to pass through a list or map. For example:

Set<int> listc = {1,2,3,4};

listc.foreach(print)

This is the most efficient way to use it, but alse you can do this:

listc.foreach((item){
	print("$item");
});

Maps

Map<String, float> accounts = {
	"111": 120.0,
	"222": 120.22,
	"333": 90.23
};

accounts.foreach((key, value){
	print("Key: $key; Value: $value");
});