Search code examples
rsymbolsreinforcement-learning

R: matrix with directional arrows

I am trying to reproduce with R an algorithm described in Sutton and Barto (2018), but I was not able to produce a matrix with arrows as the one described by the authors on page 65:

enter image description here

I tried to use the package "fields" for this purpose, but without much success.

In Python the solution proposed by Shangtong Zhang and Kenta Shimada relies on using the arrows symbols: ACTIONS_FIGS=[ '←', '↑', '→', '↓'] but this does not work nicely with R...

EDIT: I coded the initial actions and the action updates numerically as follows:

library(data.table)
action_random = data.table(cell=c(1:25))
action_random$action_up = action_random$action_right = action_random$action_down =
action_random$action_left = rep(1,25)
action_random$proba = rep(1/4,25)
action_random

I was also able to adapt the code posted here, to draw a simple grid with simple arrows:

arrows = matrix(c("\U2190","\U2191","\U2192","\U2193"),nrow=2,ncol=2)
grid_arrows = expand.grid(x=1:ncol(arrows),y=1:nrow(arrows))
grid_arrows$val = arrows[as.matrix(grid_arrows[c('y','x')])]

library(ggplot2)

ggplot(grid_arrows, aes(x=x, y=y, label=val)) + 
  geom_tile(fill='transparent', colour = 'black') + 
  geom_text(size = 14) + 
  scale_y_reverse() +
  theme_classic() + 
  theme(axis.text  = element_blank(),
        panel.grid = element_blank(),
        axis.line  = element_blank(),
        axis.ticks = element_blank(),
        axis.title = element_blank())

However:
(i) There is no unicode available for the nice 2 are 4-directional arrows reported in Table $\pi_\ast$ above
(ii) ... and so I was not trying to code the bijection between the numerical values in the Table "action_random" and a nice Table with arrows in it...

Any hint helping to resolve issues (i) and (ii) are welcome.

Solution

  • Here is a grid+lattice way to reproduce the matrix:

    library(grid)
library(lattice)

grid.newpage()
pushViewport(viewport(width = 0.8, height = 0.8)) 
grid.rect(width = 1, height = 1)
panel.grid(h = 4, v = 4)

direct = function(xCenter, yCenter, type){
  
  d= 0.05
  
  north = function(xCenter, yCenter){ 
    grid.curve(xCenter, yCenter-d ,xCenter, yCenter+d, 
               ncp = 1, angle = 90, gp=gpar(lwd=1, fill="black"),
               inflect = FALSE, shape = 0,
               arrow = arrow(type="closed", ends = "last", 
                      angle = 30, length = unit(0.2, "cm")))}
  
  west = function(xCenter, yCenter){
    grid.curve(xCenter+d, yCenter ,xCenter-d, yCenter, 
               ncp = 1, angle = 90, gp=gpar(lwd=1, fill="black"),
               inflect = FALSE, shape = 0,
               arrow = arrow(type="closed", ends = "last", 
                             angle = 30, length = unit(0.2, "cm")))}
  east = function(xCenter, yCenter){
    grid.curve(xCenter+d, yCenter ,xCenter-d, yCenter, 
               ncp = 1, angle = 90, gp=gpar(lwd=1, fill="black"),
               inflect = FALSE, shape = 0,
               arrow = arrow(type="closed", ends = "first", 
                             angle = 30, length = unit(0.2, "cm")))}
  
  northeast = function(xCenter, yCenter){
       grid.curve(xCenter-d, yCenter+d ,xCenter+d, yCenter-d, 
                 ncp = 1, angle = 90, gp=gpar(lwd=1, fill="black"),
                 inflect = FALSE, shape = 0,
                 arrow = arrow(type="closed", ends = "both", 
                         angle = 30, length = unit(0.2, "cm")))}
  
  northwest = function(xCenter, yCenter){
       grid.curve(xCenter-d, yCenter-d ,xCenter+d, yCenter+d, 
               ncp = 1, angle = 90, gp=gpar(lwd=1, fill="black"),
               inflect = FALSE, shape = 0,
               arrow = arrow(type="closed", ends = "both", 
                             angle = 30, length = unit(0.2, "cm")))}
  all = function(xCenter, yCenter){
      grid.curve(xCenter+d, yCenter ,xCenter-d, yCenter, 
                 ncp = 1, angle = 90, gp=gpar(lwd=1, fill="black"),
                 inflect = FALSE, shape = 0,
                 arrow = arrow(type="closed", ends = "both", 
                               angle = 30, length = unit(0.2, "cm")))
      grid.curve(xCenter, yCenter-d ,xCenter, yCenter+d, 
             ncp = 1, angle = 90, gp=gpar(lwd=1, fill="black"),
             inflect = FALSE, shape = 0,
             arrow = arrow(type="closed", ends = "both", 
                           angle = 30, length = unit(0.2, "cm")))}
  switch(type,
         'n' = north(xCenter, yCenter),
         'e' = east(xCenter, yCenter),
         'w' = west(xCenter, yCenter),
         'nw'= northwest(xCenter, yCenter),
         'ne' = northeast(xCenter, yCenter),
         'all' = all(xCenter, yCenter)
         )
}

x = seq(0.1, 0.9, by = 0.2)
y = x
centers = expand.grid(x0 = x, y0 = y)

row1 = row2 = row3 = c('ne','n', rep('nw',3))
row4 = c('ne','n','nw','w','w')
row5 = c('e','all','w','all','w')

dir = c(row1,row2,row3,row4,row5)
df = data.frame(centers, dir)

for (k in 1:nrow(df)) direct(df$x0[k], df$y0[k], df$dir[k])
grid.text(bquote(~pi["*"]), y = -0.05)

    enter image description here