"""Grid-based cell space implementations with different connection patterns.
Provides several grid types for organizing cells:
- OrthogonalMooreGrid: 8 neighbors in 2D, (3^n)-1 in nD
- OrthogonalVonNeumannGrid: 4 neighbors in 2D, 2n in nD
- HexGrid: 6 neighbors in hexagonal pattern (2D only)
Each grid type supports optional wrapping (torus) and cell capacity limits.
Choose based on how movement and connectivity should work in your model -
Moore for unrestricted movement, Von Neumann for orthogonal-only movement,
or Hex for more uniform distances.
"""
from __future__ import annotations
import copyreg
from collections.abc import Sequence
from itertools import product
from random import Random
from typing import Any, Generic, TypeVar
from mesa.experimental.cell_space import Cell, DiscreteSpace
from mesa.experimental.cell_space.property_layer import (
HasPropertyLayers,
PropertyDescriptor,
)
T = TypeVar("T", bound=Cell)
[docs]
def pickle_gridcell(obj):
"""Helper function for pickling GridCell instances."""
# we have the base class and the state via __getstate__
args = obj.__class__.__bases__[0], obj.__getstate__()
return unpickle_gridcell, args
[docs]
def unpickle_gridcell(parent, fields):
"""Helper function for unpickling GridCell instances."""
# since the class is dynamically created, we recreate it here
cell_klass = type(
"GridCell",
(parent,),
{"_mesa_properties": set()},
)
instance = cell_klass(
(0, 0)
) # we use a default coordinate and overwrite it with the correct value next
# __gestate__ returns a tuple with dict and slots, but slots contains the dict so we can just use the
# second item only
for k, v in fields[1].items():
if k != "__dict__":
setattr(instance, k, v)
return instance
[docs]
class Grid(DiscreteSpace[T], Generic[T], HasPropertyLayers):
"""Base class for all grid classes.
Attributes:
dimensions (Sequence[int]): the dimensions of the grid
torus (bool): whether the grid is a torus
capacity (int): the capacity of a grid cell
random (Random): the random number generator
_try_random (bool): whether to get empty cell be repeatedly trying random cell
Notes:
width and height are accessible via properties, higher dimensions can be retrieved via dimensions
"""
@property
def width(self) -> int:
"""Convenience access to the width of the grid."""
return self.dimensions[0]
@property
def height(self) -> int:
"""Convenience access to the height of the grid."""
return self.dimensions[1]
def __init__(
self,
dimensions: Sequence[int],
torus: bool = False,
capacity: float | None = None,
random: Random | None = None,
cell_klass: type[T] = Cell,
) -> None:
"""Initialise the grid class.
Args:
dimensions: the dimensions of the space
torus: whether the space wraps
capacity: capacity of the grid cell
random: a random number generator
cell_klass: the base class to use for the cells
"""
super().__init__(capacity=capacity, random=random, cell_klass=cell_klass)
self.torus = torus
self.dimensions = dimensions
self._try_random = True
self._ndims = len(dimensions)
self._validate_parameters()
self.cell_klass = type(
"GridCell",
(self.cell_klass,),
{"_mesa_properties": set()},
)
# we register the pickle_gridcell helper function
copyreg.pickle(self.cell_klass, pickle_gridcell)
coordinates = product(*(range(dim) for dim in self.dimensions))
self._cells = {
coord: self.cell_klass(coord, capacity, random=self.random)
for coord in coordinates
}
self._connect_cells()
self.create_property_layer("empty", default_value=True, dtype=bool)
def _connect_cells(self) -> None:
if self._ndims == 2:
self._connect_cells_2d()
else:
self._connect_cells_nd()
def _connect_cells_2d(self) -> None: ...
def _connect_cells_nd(self) -> None: ...
def _validate_parameters(self):
if not all(isinstance(dim, int) and dim > 0 for dim in self.dimensions):
raise ValueError("Dimensions must be a list of positive integers.")
if not isinstance(self.torus, bool):
raise ValueError("Torus must be a boolean.")
if self.capacity is not None and not isinstance(self.capacity, float | int):
raise ValueError("Capacity must be a number or None.")
[docs]
def select_random_empty_cell(self) -> T: # noqa
# FIXME:: currently just a simple boolean to control behavior
# FIXME:: basically if grid is close to 99% full, creating empty list can be faster
# FIXME:: note however that the old results don't apply because in this implementation
# FIXME:: because empties list needs to be rebuild each time
# This method is based on Agents.jl's random_empty() implementation. See
# https://github.com/JuliaDynamics/Agents.jl/pull/541. For the discussion, see
# https://github.com/projectmesa/mesa/issues/1052 and
# https://github.com/projectmesa/mesa/pull/1565. The cutoff value provided
# is the break-even comparison with the time taken in the else branching point.
if self._try_random:
while True:
cell = self.all_cells.select_random_cell()
if cell.is_empty:
return cell
else:
return super().select_random_empty_cell()
def _connect_single_cell_nd(self, cell: T, offsets: list[tuple[int, ...]]) -> None:
coord = cell.coordinate
for d_coord in offsets:
n_coord = tuple(c + dc for c, dc in zip(coord, d_coord))
if self.torus:
n_coord = tuple(nc % d for nc, d in zip(n_coord, self.dimensions))
if all(0 <= nc < d for nc, d in zip(n_coord, self.dimensions)):
cell.connect(self._cells[n_coord], d_coord)
def _connect_single_cell_2d(self, cell: T, offsets: list[tuple[int, int]]) -> None:
i, j = cell.coordinate
height, width = self.dimensions
for di, dj in offsets:
ni, nj = (i + di, j + dj)
if self.torus:
ni, nj = ni % height, nj % width
if 0 <= ni < height and 0 <= nj < width:
cell.connect(self._cells[ni, nj], (di, dj))
def __getstate__(self) -> dict[str, Any]:
"""Custom __getstate__ for handling dynamic GridCell class and PropertyDescriptors."""
state = super().__getstate__()
state = {k: v for k, v in state.items() if k != "cell_klass"}
return state
def __setstate__(self, state: dict[str, Any]) -> None:
"""Custom __setstate__ for handling dynamic GridCell class and PropertyDescriptors."""
self.__dict__ = state
self._connect_cells() # using super fails for this for some reason, so we repeat ourselves
self.cell_klass = type(
self._cells[(0, 0)]
) # the __reduce__ function handles this for us nicely
for layer in self._mesa_property_layers.values():
setattr(self.cell_klass, layer.name, PropertyDescriptor(layer))
[docs]
class OrthogonalMooreGrid(Grid[T]):
"""Grid where cells are connected to their 8 neighbors.
Example for two dimensions:
directions = [
(-1, -1), (-1, 0), (-1, 1),
( 0, -1), ( 0, 1),
( 1, -1), ( 1, 0), ( 1, 1),
]
"""
def _connect_cells_2d(self) -> None:
# fmt: off
offsets = [
(-1, -1), (-1, 0), (-1, 1),
( 0, -1), ( 0, 1),
( 1, -1), ( 1, 0), ( 1, 1),
]
# fmt: on
for cell in self.all_cells:
self._connect_single_cell_2d(cell, offsets)
def _connect_cells_nd(self) -> None:
offsets = list(product([-1, 0, 1], repeat=len(self.dimensions)))
offsets.remove((0,) * len(self.dimensions)) # Remove the central cell
for cell in self.all_cells:
self._connect_single_cell_nd(cell, offsets)
[docs]
class OrthogonalVonNeumannGrid(Grid[T]):
"""Grid where cells are connected to their 4 neighbors.
Example for two dimensions:
directions = [
(0, -1),
(-1, 0), ( 1, 0),
(0, 1),
]
"""
def _connect_cells_2d(self) -> None:
# fmt: off
offsets = [
(-1, 0),
(0, -1), (0, 1),
( 1, 0),
]
# fmt: on
for cell in self.all_cells:
self._connect_single_cell_2d(cell, offsets)
def _connect_cells_nd(self) -> None:
offsets: list[tuple[int, ...]] = []
dimensions = len(self.dimensions)
for dim in range(dimensions):
for delta in [
-1,
1,
]: # Move one step in each direction for the current dimension
offset = [0] * dimensions
offset[dim] = delta
offsets.append(tuple(offset))
for cell in self.all_cells:
self._connect_single_cell_nd(cell, offsets)
[docs]
class HexGrid(Grid[T]):
"""A Grid with hexagonal tilling of the space."""
def _connect_cells_2d(self) -> None:
# fmt: off
even_offsets = [
(-1, -1), (-1, 0),
( 0, -1), ( 0, 1),
( 1, -1), ( 1, 0),
]
odd_offsets = [
(-1, 0), (-1, 1),
( 0, -1), ( 0, 1),
( 1, 0), ( 1, 1),
]
# fmt: on
for cell in self.all_cells:
i = cell.coordinate[0]
offsets = even_offsets if i % 2 == 0 else odd_offsets
self._connect_single_cell_2d(cell, offsets=offsets)
def _connect_cells_nd(self) -> None:
raise NotImplementedError("HexGrids are only defined for 2 dimensions")
def _validate_parameters(self):
super()._validate_parameters()
if len(self.dimensions) != 2:
raise ValueError("HexGrid must have exactly 2 dimensions.")
