C++/Valarray/valarray
Содержание
- 1 Create valarray of bool value by using comparison operator on another valarray
- 2 Do sqrt for all elements in a valarray
- 3 Minus 10 from each element in a valarray
- 4 Print three-dimensional valarray line-by-line
- 5 Print valarray as two-dimensional array
- 6 Use valarray + valarray to double the value for each element in valarray
- 7 valarray with double value inside
Create valarray of bool value by using comparison operator on another valarray
<source lang="cpp">
- 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
*/ </source>
Do sqrt for all elements in a valarray
<source lang="cpp">
- 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
*/ </source>
Minus 10 from each element in a valarray
<source lang="cpp">
- 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
*/ </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. */
- 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
*/ </source>
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. */
- 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 elements 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
*/ </source>
Use valarray + valarray to double the value for each element in valarray
<source lang="cpp">
- 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
*/ </source>
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. */
- 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
*/ </source>