Dart Common Collection Methods

Most of the programming languages have arrays as a way to list items together. However, Dart has a collection of data structures similar to array. These are supported by the Dart library ‘dart : core’ and some other classes.

Such dart collections are classified as follows :

1. List : It is an ordered list of objects that is implemented using List class. This class enables the creation and manipulation of lists.
   There are following two types of lists :

• • Fixed length list : The size of this list is fixed and cannot be changed at runtime.
  • Growable list : The size of this list is dynamic and can be changed at runtime.

2. Set : It represents a collection of objects in which every object can appear only once.
3. Maps : It consists of a key-value pair that can belong to any data type. It is completely dynamic, that means it can grow and shrink at runtime.
4. Queue : It is a collection from where we can add and delete items from both ends.

Here are some of the common collection methods :

1. isEmpty( ) or isNotEmpty( ) :

These two functions are used to check whether a list, set, or map has items or not, that is, whether it is empty or not.

Consider the following example that explains the concept of these functions :

Program

void main( )

{

  // declaraing a list ' coffees '

  var coffees = [ ] ;




  // declaring a list ' teas '

  var teas = [ ' green ', ' black ', ' chamomile ', ' earl grey ' ] ;




  // checking whether the list ' coffees ' is empty or not

  print( " Is the list of coffees empty ? : " ) ;

  print( coffees.isEmpty ) ;




  // checking whether the list ' teas ' is empty or not

  print( " Is the list of teas empty ? : " ) ;

  print( teas.isEmpty ) ;

}

Output

 Is the list of coffees empty ? :

    true

    Is the list of teas empty ? :

    false

2. forEach( ) :

This function is used to apply a certain function or condition to each item in a list, set, or map.

Consider the following example that explains the concept of this  function :

Program

void main( )

{  

    // defining the list ' teas '

    var teas = [ ' green ', ' black ', ' chamomile ', ' earl grey ' ] ; 

   

    // converting the each item of the list in the upper case

    var t = teas.map( ( tea ) => tea.toUpperCase( ) ) ;




    // printing each item of the list

    t.forEach( print ) ;

}

Output:

     GREEN

     BLACK

     CHAMOMILE

     EARL GREY

3. where( ) :

This function is used to retrieve all the items that match to a particular condition listen in the where( ) function. Similarly, the functions any( ) and every( ) can be used to check whether some or each item in the list matches a condition.

Consider the following example that explains the concept of this function :

Example – 3 :

void main( )

{

   var colours = [ ' green ', ' black ', ' red ', ' white ' ] ;




  // black is the darkest colour of all listed colors

  bool isdark( String colName ) => colName == ' black ' ;




  // Use where( ) function to retrive the item that returns true

  // from the isdark( ) function.

  // Here, it returns the colour that is dark in the list

  print( colours.where( isdark ) ) ;




  // Use any( ) function to check whether any of the item in the

  // collection returns satisfies the isdark( ) function

  // Here, it returns true if any of the colour is dark in the list

  print( colours.any( isdark ) ) ;




  // Use every( ) function to check whether all the items in a

  // collection satisfies the isdark( ) function

  // Here, it returns true if every colour is dark in the list

  print( colours.every( isdark ) ) ;

}

Output :

( black )

true

false