Swaps the order of the attributes to create a new design candidate. For example, if the attributes in the first and fourth choice situation (row) are swapped, then (1, 2, 1, 3, 2, 3) becomes( 3, 2, 1, 1, 2, 3).
swap(x)The algorithm randomly samples 2 row positions with different levels that are swapped, so that every swap changes the design candidate. A column with a single level is returned unchanged.
Hensher, D. A., Rose, J. M. & Greene, W., 2005, Applied Choice Analysis, 2nd ed., Cambridge University Press