Compare Two Lists

In dart programming, Lists are used for the collection of data. We declare just variables instead of declaring a separate variable for each value of the collection. Lists are indexable so that we access the values using index ( starts from 0 ).

In this article, we will see how to compare two Lists in the dart.  For example:

a = [ 1, 2, 3, 4, 5 ]
b = [ 1, 2, 3, 4, 5 ]

//  a is equal to b

c = [ 2, 3, 7, 3, 7, 9 ]
d = [ 2, 5, 6, 9, 3, 4 ]

//  c is not equal to d

Methods:

For comparing two lists we have the following methods.

1. Using the join( ) method
2. Using forin loop
3. Using dart Collection package

1. Using the join( ) method:
Join method is used for combining all the array elements and return as a String. Using the join method the steps are following.

1. Get two Lists
2. join them
3. compare them

Implementation : 

// Implementation of array comparison using join method

void main(){
  var arr1 = [ 1, 2, 3, 4, 5, 6 ];
  var arr2 = [ 1, 2, 3, 4, 5, 6 ];
    
  // join both the array and compare them
  var comp = arr1.join() == arr2.join();
  
  // print The result
  comp == true ? print("arr1 is equal to arr2") : print("arr1 is not equal to arr2");
}

Output:

arr1 is equal to arr2

2. Using forin loop :

Using for in loop the steps of comparison of two lists are following

1. get two array
2. create a function the returns a bool and pass both the array into it
3. Using forin loop, iterate the first array
4. now on each iteration check if the element of that index is matching with the second array or not
5. if any item is not matching the return false.

Implementation:

// Implementation using forin loop


// creating a function that returns a boolean value
bool isEqual(var arr1, var arr2){
  int i = 0;
  for(var a in arr1){
    // check if the value is equal to the second array at same index or not.
    if(a != arr2[i]){
      return false;
    }
    i++;
  }
  
  // If all the index are matching then return true
  return true;
}


void main(){
  var arr1 = [ 1, 4, 2, 5, 3, 6, 3, 7, 3 ];
  var arr2 = [ 1, 4, 2, 5, 2, 6, 3, 7, 3 ];
      
  var res = isEqual(arr1, arr2);
    
  res ? print("arr1 is equal to arr2") : print("arr1 is not equal to arr2");
  
}

Output:

arr1 is not equal to arr2

3. Using dart collection package

Using the collection package you can check if two lists are equal or not. Steps for using collections following:

1. Import collection package
2. Get the Lists
3. Use IterableEquality( ) function with equals( ) method
4. inside equals( ) method pass the both lists

Implementation : 

// implementation of List comparision using collection package

import 'package:collection/collection.dart';

void main() {
    
    var arr1 = [ 1, 2, 3, 4, 5 ];
    var arr2 = [ 1, 2, 3, 4, 5 ]
      
    // check is the lists are equal
    var isEqual = ListEquality().equals(arr1, arr2);
    
    if(isEqual){
      print("arr1 is equal to arr2");
    }else{
      print("arr1 is not equal to arr2");
    }
}

Output:

arr1 is equal to arr2