3.10 Picks

Vector and matrix picks allow arbitrary elements to be selected from a vector rather than just those patterns which can be selected by subscripting. A pick is created by calling member function pick(const RWIntVec&), where RWIntVec is a typedef for RWMathVec<int>. You can think of it as subscripting with an RWIntVec instead of an int:

// Set up picked elements:
RWIntVec ipick("[3 4 8]");

RWMathVec<double> dv(10, 0, 2);     // 0 2 4 6 8 10 12 14 16 18

RWMathVecPick<double> dvPick = dv.pick(ipick);

cout << dvPick.length() << endl;    // 3
cout << dvPick(0)       << endl;    // 6
cout << dvPick(2)       << endl;    // 16

Picks can also be used as lvalues:

dvPick = -1;
cout << dv;                         // 0 2 4 -1 -1 10 12 14 -1 18

Unlike the subscripting operators, vector picks are not built into the classes, but implemented using a helper class with no public constructors. The result is that, unlike subscripting, picking does not create a new view. Because they are implemented using a helper class and their indexing is done using RWMathVec<int>s, picks are less efficient than subscripting.