RCOMM 2012 Sudoku Challenge: 2 - Drop impossible values

Process from the http://rcomm2012.org live data mining challenge. The task was to partially solve a Sudoku puzzle by solving three subtasks. Processes 1-3 in this pack are the actual solutions to the tasks, process 0 loads the required data into your repository and process 4 is the bonus that solves the entire puzzle.

IMPORTANT: Save this process as "RCOMM 2012 Sudoku Challenge: 2 - Drop impossible values" since it is included from process 3.

This process eliminates impossible rows from the table "All Possibilities" that can be excluded by looking at one row of the input data set "Sudoku Predefined". The table "All Possibilities" is defined by process 1, see the comments therein for details. The file "Sudoku Predefined" contains one predefined number in the Sudoku puzzle for row. The row x, y, z, v means that the value v occurs at column x, row y. z is the implicitly defined index of the 3x3 sub-field containing the cell x, y. The row considered by this process is defined by the macro %{example} which is set to "1" in the process context. The process starts by extracting the values of x, y, z, and v for the selected example into macros. Then, it computes a new column that determines whether a row in "All Possibilities" is still possible. That is the case if it matches on v and either x, y, or z. These examples are then removed. This process is repeatedly called by process 3 which assigns different values to the macro %{examples}.