how to record the moving direction is SAS? - macros

Question

I have a maze file which is like this.
1111111
1001111
1101101
1101001
1100011
1111111
a format $direction indicating the direction
start end label
D D down
L L left
R R right
U U up
Then, I have a dataset indicating the start and end point.
Row Column
start 2 2
end 3 6
How can I record the moving direction from the start to the end like this?
direction row column
2 2
right 2 3
down 3 3
down 4 3
down 5 3
i have use array
array m(i,j)
if m(i,j) = 0 then
row=i;
column=j;
output;
however, it simply just not in the correct moving order.
Thanks if you can help.

Answer 1

Here's one way of doing this. Writing a more generalised maze-solving algorithm using SAS data step logic is left as an exercise for the reader, but this should work for labyrinths.
/* Define the format */
proc format;
value $direction
'D' = 'down'
'L' = 'left'
'R' = 'right'
'U' = 'up'
;
run;
data want;
/*Read in the maze and start/end points in (y,x) orientation*/
array maze(6,7) (
1,1,1,1,1,1,1,
1,0,0,1,1,1,1,
1,1,0,1,1,0,1,
1,1,0,1,0,0,1,
1,1,0,0,0,1,1,
1,1,1,1,1,1,1
);
array endpoints (2,2) (
2,2
3,6
);
/*Load the start point and output a row*/
x = endpoints(1,2);
y = endpoints(1,1);
output;
/*
Navigate through the maze.
Assume for the sake of simplicity that it is really more of a labyrinth,
i.e. there is only ever one valid direction in which to move,
other than the direction you just came from,
and that the end point is reachable
*/
do _n_ = 1 by 1 until(x = endpoints(2,2) and y = endpoints(2,1));
if maze(y-1,x) = 0 and direction ne 'D' then do;
direction = 'U';
y + -1;
end;
else if maze(y+1,x) = 0 and direction ne 'U' then do;
direction = 'D';
y + 1;
end;
else if maze(y,x-1) = 0 and direction ne 'R' then do;
direction = 'L';
x + -1;
end;
else if maze(y,x+1) = 0 and direction ne 'L' then do;
direction = 'R';
x + 1;
end;
output;
if _n_ > 15 then stop; /*Set a step limit in case something goes wrong*/
end;
format direction $direction.;
drop maze: endpoints:;
run;