Ok I get what you are trying to do I think.
In your case, if you don't need a specific route name, you can just use the x index as your "route number", starting with 0 (If you do, you can use the indexof() expression).
Your conditions would include:
Array for each XY
System Compare two values Array.CurY = routeNumber
Array Compare Current Value !=0 (because you don't have the same number of monsters per route, some cells will be empty, or 0 - you don't want those)
The action would be:
randomizerArray - Push back Array.CurValue
(You only need one action because you are only pushing one value to the new array. The randomizer array should start out as 0 width, 1 height, 1 depth)
Then use floor(random(randomizerArray.Width)) to pick a random index from the randomizerArray, and reset the array by setting it back to 0 width.