std:: valarray class in C++

Difficulty Level : Medium
Last Updated : 04 May, 2020

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

This article is contributed by Manjeet Singh .If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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