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std:: valarray class in C++

C++98 introduced a special container called valarray to hold and provide mathematical operations on arrays efficiently.

  • It supports element-wise mathematical operations and various forms of generalized subscript operators, slicing and indirect access.
  • As compare to vectors, valarrays are efficient in certain mathematical operations than vectors also.

Public member functions in valarray class :

1. apply() :- This function applies the manipulation given in its arguments to all the valarray elements at once and returns a new valarray with manipulated values.

2. sum() :- This function returns the summation of all the elements of valarrays at once.

// C++ code to demonstrate the working of 
// apply() and sum()
#include<iostream>
#include<valarray> // for valarray functions
using namespace std;
int main()
{
    // Initializing valarray
    valarray<int> varr = { 10, 2, 20, 1, 30 };
      
    // Declaring new valarray
    valarray<int> varr1 ;
      
    // Using apply() to increment all elements by 5
    varr1 = varr.apply([](int x){return x=x+5;});
      
    // Displaying new elements value
    cout << "The new valarray with manipulated values is : ";
    for (int &x: varr1) cout << x << " ";
    cout << endl;
      
    // Displaying sum of both old and new valarray
    cout << "The sum of old valarray is : ";
    cout << varr.sum() << endl;
    cout << "The sum of new valarray is : ";
    cout << varr1.sum() << endl;
  
    return 0;
      
}

Output:



The new valarray with manipulated values is : 15 7 25 6 35 
The sum of old valarray is : 63
The sum of new valarray is : 88

3. min() :- This function returns the smallest element of valarray.

4. max() :- This function returns the largest element of valarray.

// C++ code to demonstrate the working of 
// max() and min()
#include<iostream>
#include<valarray> // for valarray functions
using namespace std;
int main()
{
    // Initializing valarray
    valarray<int> varr = { 10, 2, 20, 1, 30 };
      
    // Displaying largest element of valarray
    cout << "The largest element of valarray is : ";
    cout << varr.max() << endl;
      
    // Displaying smallest element of valarray
    cout << "The smallest element of valarray is : ";
    cout << varr.min() << endl;
  
    return 0;
      
}

Output:

The largest element of valarray is : 30
The smallest element of valarray is : 1

5. shift() :- This function returns the new valarray after shifting elements by the number mentioned in its argument. If the number is positive, left-shift is applied, if number is negative, right-shift is applied.

6. cshift() :- This function returns the new valarray after circularly shifting(rotating) elements by the number mentioned in its argument. If the number is positive, left-circular shift is applied, if number is negative, right-circular shift is applied.

// C++ code to demonstrate the working of 
// shift() and cshift()
#include<iostream>
#include<valarray> // for valarray functions
using namespace std;
int main()
{
    // Initializing valarray
    valarray<int> varr = { 10, 2, 20, 1, 30 };
      
    // Declaring new valarray
    valarray<int> varr1;
      
    // using shift() to shift elements to left
    // shifts valarray by 2 position
    varr1 = varr.shift(2);
      
    // Displaying elements of valarray after shifting
    cout << "The new valarray after shifting is : ";
    for ( int&x : varr1) cout << x << " ";
    cout << endl;
      
    // using cshift() to circulary shift elements to right
    // rotates valarray by 3 position
    varr1 = varr.cshift(-3);
      
    // Displaying elements of valarray after circular shifting
    cout << "The new valarray after circular shifting is : ";
    for ( int&x : varr1) cout << x << " ";
    cout << endl;
  
    return 0;
      
}

Output:

The new valarray after shifting is : 20 1 30 0 0 
The new valarray after circular shifting is : 20 1 30 10 2 

7. swap() :- This function swaps one valarray with other.

// C++ code to demonstrate the working of 
// swap()
#include<iostream>
#include<valarray> // for valarray functions
using namespace std;
int main()
{
   // Initializing 1st valarray
    valarray<int> varr1 = {1, 2, 3, 4};
       
    // Initializing 2nd valarray
    valarray<int> varr2 = {2, 4, 6, 8};
       
     // Displaying valarrays before swapping
     cout << "The contents of 1st valarray "
             "before swapping are : ";
     for (int &x : varr1)
         cout << x << " ";
     cout << endl;
     cout << "The contents of 2nd valarray "
             "before swapping are : ";
     for (int &x : varr2)
         cout << x << " ";
     cout << endl;
    
     // Use of swap() to swap the valarrays
     varr1.swap(varr2);
    
     // Displaying valarrays after swapping
     cout << "The contents of 1st valarray "
             "after swapping are : ";
     for (int &x : varr1)
         cout << x << " ";
     cout << endl;
    
     cout << "The contents of 2nd valarray "
             "after swapping are : ";
     for (int &x : varr2)
         cout << x << " ";
     cout << endl;
  
    return 0;
      
}

Output:

The contents of 1st valarray before swapping are : 1 2 3 4 
The contents of 2nd valarray before swapping are : 2 4 6 8 
The contents of 1st valarray after swapping are : 2 4 6 8 
The contents of 2nd valarray after swapping are : 1 2 3 4 

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This article is attributed to GeeksforGeeks.org

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