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import sys
from six import StringIO
from gym import utils
from gym.envs.toy_text import discrete
import numpy as np
MAP = [
"+---------+",
"|R: | : :G|",
"| : : : : |",
"| : : : : |",
"| | : | : |",
"|Y| : |B: |",
"+---------+",
]
class TaxiEnv(discrete.DiscreteEnv):
"""
The Taxi Problem
from "Hierarchical Reinforcement Learning with the MAXQ Value Function Decomposition"
by Tom Dietterich
Description:
There are four designated locations in the grid world indicated by R(ed), B(lue), G(reen), and Y(ellow). When the episode starts, the taxi starts off at a random square and the passenger is at a random location. The taxi drive to the passenger's location, pick up the passenger, drive to the passenger's destination (another one of the four specified locations), and then drop off the passenger. Once the passenger is dropped off, the episode ends.
Observations:
There are 500 discrete actions since there are 25 taxi positions, 5 possible locations of the passenger (including the case when the passenger is the taxi), and 4 destination locations.
Actions:
There are 6 discrete deterministic actions:
- 0: move south
- 1: move north
- 2: move east
- 3: move west
- 4: pickup passenger
- 5: dropoff passenger
Rewards:
There is a reward of -1 for each action and an additional reward of +20 for delievering the passenger. There is a reward of -10 for executing actions "pickup" and "dropoff" illegally.
Rendering:
- blue: passenger
- magenta: destination
- yellow: empty taxi
- green: full taxi
- other letters: locations
"""
metadata = {'render.modes': ['human', 'ansi']}
def __init__(self):
self.desc = np.asarray(MAP,dtype='c')
self.locs = locs = [(0,0), (0,4), (4,0), (4,3)]
nS = 500
nR = 5
nC = 5
maxR = nR-1
maxC = nC-1
isd = np.zeros(nS)
nA = 6
P = {s : {a : [] for a in range(nA)} for s in range(nS)}
for row in range(5):
for col in range(5):
for passidx in range(5):
for destidx in range(4):
state = self.encode(row, col, passidx, destidx)
if passidx < 4 and passidx != destidx:
isd[state] += 1
for a in range(nA):
# defaults
newrow, newcol, newpassidx = row, col, passidx
reward = -1
done = False
taxiloc = (row, col)
if a==0:
newrow = min(row+1, maxR)
elif a==1:
newrow = max(row-1, 0)
if a==2 and self.desc[1+row,2*col+2]==b":":
newcol = min(col+1, maxC)
elif a==3 and self.desc[1+row,2*col]==b":":
newcol = max(col-1, 0)
elif a==4: # pickup
if (passidx < 4 and taxiloc == locs[passidx]):
newpassidx = 4
else:
reward = -10
elif a==5: # dropoff
if (taxiloc == locs[destidx]) and passidx==4:
done = True
reward = 20
elif (taxiloc in locs) and passidx==4:
newpassidx = locs.index(taxiloc)
else:
reward = -10
newstate = self.encode(newrow, newcol, newpassidx, destidx)
P[state][a].append((1.0, newstate, reward, done))
isd /= isd.sum()
discrete.DiscreteEnv.__init__(self, nS, nA, P, isd)
def encode(self, taxirow, taxicol, passloc, destidx):
# (5) 5, 5, 4
i = taxirow
i *= 5
i += taxicol
i *= 5
i += passloc
i *= 4
i += destidx
return i
def decode(self, i):
out = []
out.append(i % 4)
i = i // 4
out.append(i % 5)
i = i // 5
out.append(i % 5)
i = i // 5
out.append(i)
assert 0 <= i < 5
return reversed(out)
def render(self, mode='human'):
outfile = StringIO() if mode == 'ansi' else sys.stdout
out = self.desc.copy().tolist()
out = [[c.decode('utf-8') for c in line] for line in out]
taxirow, taxicol, passidx, destidx = self.decode(self.s)
def ul(x): return "_" if x == " " else x
if passidx < 4:
out[1+taxirow][2*taxicol+1] = utils.colorize(out[1+taxirow][2*taxicol+1], 'yellow', highlight=True)
pi, pj = self.locs[passidx]
out[1+pi][2*pj+1] = utils.colorize(out[1+pi][2*pj+1], 'blue', bold=True)
else: # passenger in taxi
out[1+taxirow][2*taxicol+1] = utils.colorize(ul(out[1+taxirow][2*taxicol+1]), 'green', highlight=True)
di, dj = self.locs[destidx]
out[1+di][2*dj+1] = utils.colorize(out[1+di][2*dj+1], 'magenta')
outfile.write("\n".join(["".join(row) for row in out])+"\n")
if self.lastaction is not None:
outfile.write(" ({})\n".format(["South", "North", "East", "West", "Pickup", "Dropoff"][self.lastaction]))
else: outfile.write("\n")
# No need to return anything for human
if mode != 'human':
return outfile