C++ Tutorial/valarray/valarray — различия между версиями
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Версия 14:21, 25 мая 2010
Содержание
- 1 Create valarray of bool value by using comparison operator on another valarray
- 2 Do sqrt for all elements in a valarray
- 3 Get square root of elements in a valarray
- 4 Minus 10 from each element in a valarray
- 5 Plus two valarrays together
- 6 Print three-dimensional valarray line-by-line
- 7 Print valarray as two-dimensional array
- 8 subtracting 10 from each element
- 9 Use valarray + valarray to double the value for each element in valarray
- 10 valarray with double value inside
Create valarray of bool value by using comparison operator on another valarray
#include <iostream>
#include <valarray>
#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;
}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
#include <iostream>
#include <valarray>
#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;
}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
#include <iostream>
#include <valarray>
#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;
}Minus 10 from each element in a valarray
#include <iostream>
#include <valarray>
#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;
}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
#include <iostream>
#include <valarray>
#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;
}Print three-dimensional valarray line-by-line
/* 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.
*/
#include <iostream>
#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);
}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
/* 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.
*/
#include <iostream>
#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);
}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
#include <iostream>
#include <valarray>
#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;
}Use valarray + valarray to double the value for each element in valarray
#include <iostream>
#include <valarray>
#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;
}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
/* 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.
*/
#include <iostream>
#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);
}0 1 2 3 4 5 6 7 8 9 10 11 77 77 77 77 77 5 106 107 108 9 10 11
