`bit::matrix` — Swap Two Rows/Columns

Swap any two rows or columns in a bit-matrix — a standard operation in some matrix transformation algorithms.

1constexpr bit::matrix &swap_rows(std::size_t i0, std::size_t i1);
2constexpr bit::matrix &swap_cols(std::size_t j0, std::size_t j1);

1: Swap rows i0 and i1.
2: Swap columns j0 and j1.

These methods return a reference to *this, so can be chained with other calls.

Generally, these methods do not check whether the indices are in bounds. If they aren’t, the behaviour is undefined (but bound to be wrong!) All of them will perform range checking if you set the BIT_VERIFY at compile time. See bit_verify.

Example

#include <bit/bit.h>
int main()
{
1    bit::matrix<> m(4, 8, [](std::size_t i, std::size_t j) { return (i + j)%2; });
    std::cout << "Original:\n"              << m << '\n';
    std::cout << "Swapped first 2 rows:\n"  << m.swap_rows(0,1) << '\n';
    std::cout << "And back:\n"              << m.swap_rows(0,1) << '\n';
    std::cout << "Swapped first 2 cols:\n"  << m.swap_cols(0,1) << '\n';
    std::cout << "And back:\n"              << m.swap_cols(0,1) << '\n';
}

1: Set up a bit-matrix with a checkerboard pattern of zeros and ones.

Output

Original:
│0 1 0 1 0 1 0 1│
│1 0 1 0 1 0 1 0│
│0 1 0 1 0 1 0 1│
│1 0 1 0 1 0 1 0│
Swapped first 2 rows:
│1 0 1 0 1 0 1 0│
│0 1 0 1 0 1 0 1│
│0 1 0 1 0 1 0 1│
│1 0 1 0 1 0 1 0│
And back:
│0 1 0 1 0 1 0 1│
│1 0 1 0 1 0 1 0│
│0 1 0 1 0 1 0 1│
│1 0 1 0 1 0 1 0│
Swapped first 2 cols:
│1 0 0 1 0 1 0 1│
│0 1 1 0 1 0 1 0│
│1 0 0 1 0 1 0 1│
│0 1 1 0 1 0 1 0│
And back:
│0 1 0 1 0 1 0 1│
│1 0 1 0 1 0 1 0│
│0 1 0 1 0 1 0 1│
│1 0 1 0 1 0 1 0│

See Also