C++ Tutorial/valarray/valarray slice

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gslice of valarray

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

  1. include <valarray>

using namespace std;

int main() {

 valarray<int> v(12), result;
 valarray<size_t> len(2), interval(2);
 unsigned int i;
  
 for(i=0; i<12; i++) v[i] = i;
  
 len[0] = 3; len[1] = 3;
 interval[0] = 2; interval[1] = 3;
  
 cout << "Contents of v: ";
 for(i=0; i<12; i++)
   cout << v[i] << " ";
 cout << endl;
  
 result = v[gslice(0,len,interval)];
  
 cout << "Contents of result: ";
 for(i=0; i<result.size(); i++)
   cout << result[i] << " ";
  
 return 0;

}</source>

The slice and gslice Classes

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

  1. include <valarray>

using namespace std;

int main() {

 valarray<int> v(10), result;
 unsigned int i;
  
 for(i=0; i<10; i++) v[i] = i;
  
 cout << "Contents of v: ";
 for(i=0; i<10; i++)
   cout << v[i] << " ";
 cout << endl;
  
 result = v[slice(0,5,2)];
  
 cout << "Contents of result: ";
 for(i=0; i<result.size(); i++)
   cout << result[i] << " ";
  
 return 0;

}</source>

valarray slice

<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);
   // first column = second column raised to the third column
   va[slice(0,4,3)] = pow (valarray<double>(va[slice(1,4,3)]),
                           valarray<double>(va[slice(2,4,3)]));
   printValarray (va, 3);
   // create valarray with three times the third element of va
   valarray<double> vb(va[slice(2,4,0)]);
   // multiply the third column by the elements of vb
   va[slice(2,4,3)] *= vb;
   printValarray (va, 3);
   // print the square root of the elements in the second row
   printValarray (sqrt(valarray<double>(va[slice(3,3,1)])));
   // double the elements in the third row
   va[slice(2,4,3)] = valarray<double>(va[slice(2,4,3)]) * 2.0;
   printValarray (va, 3);

}</source>

0 1 2
3 4 5
6 7 8
9 10 11
1 1 2
1024 4 5
5.7648e+006 7 8
1e+011 10 11
1 1 4
1024 4 10
5.7648e+006 7 16
1e+011 10 22
1 1 8
1024 4 20
5.7648e+006 7 32
1e+011 10 44