C++ Tutorial/valarray/valarray

Create valarray of bool value by using comparison operator on another valarray

<source lang="cpp">#include <iostream>

1. include <valarray>
2. include <cmath>

using namespace std; int main() {

 valarray<int> v(10);
 for(int i=0; i<10; i++)
     v[i] = i;
 cout << "Original contents: ";
 for(int i=0; i<10; i++)
   cout << v[i] << " ";
 valarray<bool> vb = v < 5;
 cout << "Those elements less than 5: ";
 for(int i=0; i<10; i++)
   cout << vb[i] << " ";
 cout << endl;

}</source>

Original contents: 0 1 2 3 4 5 6 7 8 9 Those elements less than 5: 1 1 1 1 1 0 0 0 0 0

Do sqrt for all elements in a valarray

<source lang="cpp">#include <iostream>

1. include <valarray>
2. include <cmath>

using namespace std; int main() {

 valarray<int> v(10);
 for(int i=0; i<10; i++)
     v[i] = i*i;
 cout << "Original contents: ";
 for(int i=0; i<10; i++)
   cout << v[i] << " \n\n";
 v = sqrt(v);
 for(int i=0; i<10; i++)
   cout << v[i] << " \n\n";

 cout << endl;

}</source>

Original contents: 0
1
4
9
16
25
36
49
64
81
0
1
2
3
4
5
6
7
8
9

Get square root of elements in a valarray

<source lang="cpp">#include <iostream>

1. include <valarray>
2. include <cmath>

using namespace std;

int main() {

 valarray<int> v(10);
 int i;
  
 for(i=0; i<10; i++) v[i] = i;
  
 cout << "Original contents: ";
 for(i=0; i<10; i++)
   cout << v[i] << " ";
 cout << endl;
  
 v = v.cshift(3);
  
 cout << "Shifted contents: ";
 for(i=0; i<10; i++)
   cout << v[i] << " ";
 cout << endl;
  
 valarray<double> fv(5);
 for(i=0; i<5; i++) fv[i] = (double) i;
  
 cout << "Original contents: ";
 for(i=0; i<5; i++)
   cout << fv[i] << " ";
 cout << endl;
  
 fv = sqrt(fv);
  
 cout << "Square roots: ";
 for(i=0; i<5; i++)
   cout << fv[i] << " ";
 cout << endl;
  
  
 return 0;

}</source>

Minus 10 from each element in a valarray

<source lang="cpp">#include <iostream>

1. include <valarray>
2. include <cmath>

using namespace std; int main() {

 valarray<int> v(10);
 for(int i=0; i<10; i++)
     v[i] = i;
 cout << "Original contents: ";
 for(int i=0; i<10; i++)
   cout << v[i] << " \n\n";
 v = v - 10;
 for(int i=0; i<10; i++)
   cout << v[i] << " \n\n";

 cout << endl;

}</source>

Original contents: 0
1
2
3
4
5
6
7
8
9
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1

Plus two valarrays together

<source lang="cpp">#include <iostream>

1. include <valarray>
2. include <cmath>

using namespace std;

int main() {

 valarray<int> v(10);
 int i;
  
 for(i=0; i<10; i++) v[i] = i;
  
 cout << "Original contents: ";
 for(i=0; i<10; i++)
   cout << v[i] << " ";
 cout << endl;
  
 valarray<double> fv(5);
 for(i=0; i<5; i++) fv[i] = (double) i;
  
 cout << "Original contents: ";
 for(i=0; i<5; i++)
   cout << fv[i] << " ";
 cout << endl;
  
 fv = sqrt(fv);
  
 cout << "Square roots: ";
 for(i=0; i<5; i++)
   cout << fv[i] << " ";
 cout << endl;
  
 fv = fv + fv;
 cout << "Double the square roots: ";
 for(i=0; i<5; i++)
   cout << fv[i] << " ";
 cout << endl;
  
  
 return 0;

}</source>

Print three-dimensional valarray line-by-line

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <valarray>

using namespace std; // print three-dimensional valarray line-by-line template<class T> void printValarray3D (const valarray<T>& va, int dim1, int dim2) {

   for (int i=0; i<va.size()/(dim1*dim2); ++i) {
       for (int j=0; j<dim2; ++j) {
           for (int k=0; k<dim1; ++k) {
               cout << va[i*dim1*dim2+j*dim1+k] << " ";
           }
           cout << "\n";
       }
       cout << "\n";
   }
   cout << endl;

} int main() {

   /* valarray with 24 elements
    * - two groups
    * - four rows
    * - three columns
    */
   valarray<double> va(24);
   // fill valarray with values
   for (int i=0; i<24; i++) {
       va[i] = i;
   }
   // print valarray
   printValarray3D (va, 3, 4);
   // we need two two-dimensional subsets of three times 3 values
   // in two 12-element arrays
   size_t lengthvalues[] = {  2, 3 };
   size_t stridevalues[] = { 12, 3 };
   valarray<size_t> length(lengthvalues,2);
   valarray<size_t> stride(stridevalues,2);
   // assign the second column of the first three rows
   // to the first column of the first three rows
   va[gslice(0,length,stride)]
       = valarray<double>(va[gslice(1,length,stride)]);
   // add and assign the third of the first three rows
   // to the first of the first three rows
   va[gslice(0,length,stride)]
       += valarray<double>(va[gslice(2,length,stride)]);
   
   // print valarray
   printValarray3D (va, 3, 4);

}</source>

0 1 2
3 4 5
6 7 8
9 10 11
12 13 14
15 16 17
18 19 20
21 22 23

3 1 2
9 4 5
15 7 8
9 10 11
27 13 14
33 16 17
39 19 20
21 22 23

Print valarray as two-dimensional array

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <valarray>

using namespace std; // print valarray as two-dimensional array template<class T> void printValarray (const valarray<T>& va, int num) {

   for (int i=0; i<va.size()/num; i++) {
       for (int j=0; j<num; j++) {
           cout << va[i*num+j] << " ";
       }
       cout << endl;
   }
   cout << endl;

} int main() {

   // create valarray for 12 elements
   valarray<double> va(12);
   // initialize valarray by values 1.01, 2.02, ... 12.12
   for (int i=0; i<12; i++) {
       va[i] = (i+1) * 1.01;
   }
   printValarray(va,4);
   /* create array of indexes
    * - note: element type has to be size_t
    */
   valarray<size_t> idx(4);
   idx[0] = 8;
   idx[1] = 0;
   idx[2] = 3;
   idx[3] = 7;
   // use array of indexes to print the ninth, first, fourth, and eighth eleme

nts

   printValarray(valarray<double>(va[idx]), 4);
   // change the first and fourth elements and print them again indirectly
   va[0] = 11.11;
   va[3] = 44.44;
   printValarray(valarray<double>(va[idx]), 4);
   // now select the second, third, sixth, and ninth elements
   // and assign 99 to them
   idx[0] = 1;
   idx[1] = 2;
   idx[2] = 5;
   idx[3] = 8;
   va[idx] = 99;
   // print the whole valarray again
   printValarray (va, 4);

}</source>

1.01 2.02 3.03 4.04
5.05 6.06 7.07 8.08
9.09 10.1 11.11 12.12
9.09 1.01 4.04 8.08
9.09 11.11 44.44 8.08
11.11 99 99 44.44
5.05 99 7.07 8.08
99 10.1 11.11 12.12

subtracting 10 from each element

<source lang="cpp">#include <iostream>

1. include <valarray>
2. include <cmath>

using namespace std;

int main() {

 valarray<int> v(10);
 int i;
  
 for(i=0; i<10; i++) v[i] = i;
  
 cout << "Original contents: ";
 for(i=0; i<10; i++)
   cout << v[i] << " ";
 cout << endl;
  
 valarray<bool> vb = v < 5;
 cout << "Those elements less than 5: ";
 for(i=0; i<10; i++)
   cout << vb[i] << " ";
 cout << endl << endl;
  
 valarray<double> fv(5);
 for(i=0; i<5; i++) fv[i] = (double) i;
  
 cout << "Original contents: ";
 for(i=0; i<5; i++)
   cout << fv[i] << " ";
 cout << endl;
  
 fv = sqrt(fv);
  
 cout << "Square roots: ";
 for(i=0; i<5; i++)
   cout << fv[i] << " ";
 cout << endl;
  
 fv = fv - 10.0;
 cout << "After subtracting 10 from each element:\n";
 for(i=0; i<5; i++)
   cout << fv[i] << " ";
 cout << endl;
  
 return 0;

}</source>

Use valarray + valarray to double the value for each element in valarray

<source lang="cpp">#include <iostream>

1. include <valarray>
2. include <cmath>

using namespace std; int main() {

 valarray<int> v(10);
 for(int i=0; i<10; i++)
     v[i] = i;
 cout << "Original contents: ";
 for(int i=0; i<10; i++)
   cout << v[i] << " \n\n";
 v = v + v;
 for(int i=0; i<10; i++)
   cout << v[i] << " \n\n";

 cout << endl;

}</source>

Original contents: 0
1
2
3
4
5
6
7
8
9
0
2
4
6
8
10
12
14
16
18

valarray with double value inside

<source lang="cpp">/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <valarray>

using namespace std; // print valarray line-by-line template<class T> void printValarray (const valarray<T>& va, int num) {

   for (int i=0; i<va.size()/num; ++i) {
       for (int j=0; j<num; ++j) {
           cout << va[i*num+j] << " ";
       }
       cout << endl;
   }
   cout << endl;

} int main() {

   /* valarray with 12 elements
    * - four rows
    * - three columns
    */
   valarray<double> va(12);
   // fill valarray with values
   for (int i=0; i<12; i++) {
       va[i] = i;
   }
   printValarray (va, 3);
   // assign 77 to all values that are less than 5
   va[va<5.0] = 77.0;
   // add 100 to all values that are greater than 5 and less than 9
   va[va>5.0 && va<9.0] = valarray<double>(va[va>5.0 && va<9.0]) + 100.0;
   printValarray (va, 3);

}</source>

0 1 2
3 4 5
6 7 8
9 10 11
77 77 77
77 77 5
106 107 108
9 10 11