[Bug Report] FlatObsWrapper lets to Crashes Due to Concatenation of uint8 and float32 Arrays in observation Method

[MarcSpeckmann]

If you are submitting a bug report, please fill in the following details and use the tag [bug].

Describe the bug
The minigrid.wrappers.The FlatObsWrapper class in the observation method concatenates a uint8 array and a float32 array. This leads to RLlib crashes due to the mix of different dtypes.

Code example

System Info
Describe the characteristics of your environment:

• MiniGrid was installed via pip inside a conda env
• CentOS Linux release 7.6.1810 (Core)
• python=3.10.14

torch==2.2.0
ray[all]==2.23.0
minigrid==2.3.1
networkx==3.2.1
gputil==1.4.0
hydra_core==1.3.2
hydra-callbacks==0.5.1

Additional context

Minigrid/minigrid/wrappers.py

Lines 590 to 624 in 37f28b2

	def observation(self, obs):
	image = obs["image"]
	mission = obs["mission"]
	# Cache the last-encoded mission string
	if mission != self.cachedStr:
	assert (
	len(mission) <= self.maxStrLen
	), f"mission string too long ({len(mission)} chars)"
	mission = mission.lower()
	strArray = np.zeros(
	shape=(self.maxStrLen, self.numCharCodes), dtype="float32"
	)
	for idx, ch in enumerate(mission):
	if ch >= "a" and ch <= "z":
	chNo = ord(ch) - ord("a")
	elif ch == " ":
	chNo = ord("z") - ord("a") + 1
	elif ch == ",":
	chNo = ord("z") - ord("a") + 2
	else:
	raise ValueError(
	f"Character {ch} is not available in mission string."
	)
	assert chNo < self.numCharCodes, "%s : %d" % (ch, chNo)
	strArray[idx, chNo] = 1
	self.cachedStr = mission
	self.cachedArray = strArray
	obs = np.concatenate((image.flatten(), self.cachedArray.flatten()))
	return obs

Checklist

• [ x] I have checked that there is no similar issue in the repo (required)

[pseudo-rnd-thoughts]

Could you provide a script to recreate the error? If possible without RLLib, just the environment and wrapper stack with the error on reset or step

[MarcSpeckmann]

Certainly! Below is a simplified example script.

import gymnasium
import minigrid
from minigrid.wrappers import FlatObsWrapper

env = FlatObsWrapper(gymnasium.make("MiniGrid-Empty-5x5-v0"))
observation, info = env.reset(seed=42)
print(env.observation_space.dtype)
print(observation.dtype)
assert env.observation_space.dtype == observation.dtype

uint8
float32
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
Cell In[8], [line 9](vscode-notebook-cell:?execution_count=8&line=9)
      [7](vscode-notebook-cell:?execution_count=8&line=7) print(env.observation_space.dtype)
      [8](vscode-notebook-cell:?execution_count=8&line=8) print(observation.dtype)
----> [9](vscode-notebook-cell:?execution_count=8&line=9) assert env.observation_space.dtype == observation.dtype

AssertionError: