indirect_array Class
The latest version of this topic can be found at indirect_array Class.
An internal, auxiliary template class that supports objects that are subsets of valarrays by providing operations between subset arrays defined by specifying a subset of indices of a parent valarray.
Syntax
Remarks
The class describes an object that stores a reference to an object va of class valarray<Type>, along with an object xa of class valarray<size_t>, which describes the sequence of elements to select from the valarray<Type> object.
You construct an indirect_array<Type> object only by writing an expression of the form va[xa]. The member functions of class indirect_array then behave like the corresponding function signatures defined for valarray<Type>, except that only the sequence of selected elements is affected.
The sequence consists of xa.size elements, where element I becomes the index xa[ I] within va.
Example:
// indirect_array.cpp
// compile with: /EHsc
#include <valarray>
#include <iostream>
int main( )
{
using namespace std;
int i;
valarray<int> va ( 10 );
for ( i = 0 ; i < 10 ; i += 2 )
va [ i ] = i;
for ( i = 1 ; i < 10 ; i += 2 )
va [ i ] = -1;
cout << "The initial operand valarray is: ( ";
for ( i = 0 ; i < 10 ; i++ )
cout << va [ i ] << " ";
cout << ")." << endl;
// Select 2nd, 4th & 6th elements
// and assign a value of 10 to them
valarray<size_t> indx ( 3 );
indx [0] = 2;
indx [1] = 4;
indx [2] = 6;
va[indx] = 10;
cout << "The modified operand valarray is: ( ";
for (i = 0 ; i < 10 ; i++ )
cout << va [ i ] << " ";
cout << ")." << endl;
}
Output
The initial operand valarray is: (0 -1 2 -1 4 -1 6 -1 8 -1).
The modified operand valarray is: (0 -1 10 -1 10 -1 10 -1 8 -1).
Requirements
Header: <valarray>
Namespace: std