Linq- Aggregate function

Aggregate Function:

To get a comma separated list of countries.

string[] Countries = {“India”, “US”, “UK”, “Canada”,” Australia”};

1.   Without Linq

string result = string.empty;

for(int i=0; I < Countries.Length; i++)

  {

     result = result + Countries[i] + “, ” ;

  }

      int lastIndex = result. LastIndexOf(“, ”);

      result =  result.Remove(lastIndex)

2.   With Linq

string result = Countries.Aggregate( (a,b) => a + “, “ + b);

How Aggregate() function works?
Step 1. First "India" is concatenated with "US" to produce result "India, US"
Step 2. Result in Step 1 is then concatenated with "UK" to produce result "India, US, UK"
Step 3: Result in Step 2 is then concatenated with "Canada" to produce result "India, US, UK, Canada"

This goes on until the last element in the array to produce the final single string "India, US, UK, Canada, Australia"

Similarly, To compute the product of all numbers in an Int Array.

int[] numbers = {2,3,4,5 };

int result = numbers.Aggregate( (a,b) => a*b);

We can also provide a seed parameter in Aggregate Function.

int result = numbers.Aggregate(10, (a,b) => a*b);

 //then result will be:1200 bcoz ((((10*2)*3)*4)*5)

// this seed value will be multiplied by every value of the array.

Step 1: Multiply (10X2) to produce result 20
Step 2: Result (20) in Step 1 is then multiplied with 3 (20X3) to produce result 60
Step 3: Result (60) in Step 2 is then multiplied with 4 (60X4) to produce result 240
Step 4: Result (240) in Step 3 is then multiplied with 5 (240X5) to produce final result 1200

List<int> numbers =  new List<int> {1,2,3,….10};

Func<int,bool> mypredicate =  x=> x%2 == 0;

IEnumerable<int> evenNum = numbers.Where(mypredicate);

or

we can create a function which returns  a Boolean and replace the mypredicate above.

          Private static bool IsEven (int number)

                {

                        if (number % 2 ==0 )

                                {

                                    return true;

}

                        else{

           return false;

}   

//or simply use :

                         //return number % 2 == 0;

                             

}

So, now we can use

IEnumerable<int> evenNums = numbers.Where(x => IsEven(x));

or

IEnumerable<int> evenNums = from a in numbers

                                                Where a % 2 ==0

                                                 Select a;

To Print the numbers and their indexes.

List<int> numbers = new List<int> {1,2,3,4,……10};

var result = numbers.Select( (num,idx) => new {TheNumber = num, TheIDX = idx});

foreach(var item in result)

{

    C.W (item.TheNumber  + “   ---    “    + item.TheIDX )

 }

And to find the Numbers & Indexes of all even numbers.

var result = numbers

                 .Select( (num,idx) => new {TheNumber = num, Theidx = idx})

                 .Where (x=> x.TheNumber % 2 ==0);

And to find only the indexes of Even numbers.

var result = numbers

                 .Select( (num,idx) => new {TheNumber = num, Theidx = idx})

 .Where (x=> x.TheNumber % 2 ==0);

                  .Select(x=> x.TheIdx) ;

Linq Standard Query operators, also called as Linq Extension methods, can be broadly classified into following categories ie.  Aggregate Operators, Generation, Grouping, Query Execution, Restriction, Join, Projection, Custom Sequence, Set, Quantifiers, Partitioning, Conversion, Miscellaneous Operators.

int[] numbers = {1,2,3,4,5,6,7,8,9,10};

int smallestNum = numbers.Min();

int smallestEvenNum = numbers.where(n=> n%2 ==0).Min();

int largestNum = numbers.Max();

int largestEvenNum = numbers.where(n=> n%2 ==0).Max();

int sumOfAllNums = numbers.Sum();

int sumOfAllEvenNums = numbers.where(n=> n%2 ==0).Sum();

int countOfAllNums = numbers.Count();

int countOfAllEvenNums = numbers.where(n=> n%2 ==0).Count();

double averageOfAllNums = numbers.Average();

double averageOfAllEvenNums = numbers.where(n=> n%2 ==0).Average();

string[] Countries = {“India”, “USA”, “UK”, “Canada”};

int minCount = Countries.Min(x=> x.Length);

int maxCount = Countries.Max(x=> x.Length);

C.W(“Shortest country name has {0} characters”, minCount);

C.W(“Longest country name has {0} characters”, maxCount);

Posted in: LINQ