from brian2.core.base import weakproxy_with_fallback
from brian2.core.spikesource import SpikeSource
from brian2.core.variables import Variables
from .group import Group, Indexing
__all__ = ["Subgroup"]
[docs]
class Subgroup(Group, SpikeSource):
"""
Subgroup of any `Group`
Parameters
----------
source : SpikeSource
The source object to subgroup.
start, stop : int
Select only spikes with indices from ``start`` to ``stop-1``.
name : str, optional
A unique name for the group, or use ``source.name+'_subgroup_0'``, etc.
"""
def __init__(self, source, start, stop, name=None):
# A Subgroup should never be constructed from another Subgroup
# Instead, use Subgroup(source.source,
# start + source.start, stop + source.start)
assert not isinstance(source, Subgroup)
self.source = weakproxy_with_fallback(source)
# Store a reference to the source's equations (if any)
self.equations = None
if hasattr(self.source, "equations"):
self.equations = weakproxy_with_fallback(self.source.equations)
if name is None:
name = f"{source.name}_subgroup*"
# We want to update the spikes attribute after it has been updated
# by the parent, we do this in slot 'thresholds' with an order
# one higher than the parent order to ensure it takes place after the
# parent threshold operation
Group.__init__(
self,
clock=source._clock,
when="thresholds",
order=source.order + 1,
name=name,
)
self._N = stop - start
self.start = start
self.stop = stop
self.events = self.source.events
# All the variables have to go via the _sub_idx to refer to the
# appropriate values in the source group
self.variables = Variables(self, default_index="_sub_idx")
# overwrite the meaning of N and i
if self.start > 0:
self.variables.add_constant("_offset", value=self.start)
self.variables.add_reference("_source_i", source, "i")
self.variables.add_subexpression(
"i",
dtype=source.variables["i"].dtype,
expr="_source_i - _offset",
index="_idx",
)
else:
# no need to calculate anything if this is a subgroup starting at 0
self.variables.add_reference("i", source)
self.variables.add_constant("N", value=self._N)
self.variables.add_constant("_source_N", value=len(source))
# add references for all variables in the original group
self.variables.add_references(source, list(source.variables.keys()))
# Only the variable _sub_idx itself is stored in the subgroup
# and needs the normal index for this group
self.variables.add_arange(
"_sub_idx", size=self._N, start=self.start, index="_idx"
)
# special indexing for subgroups
self._indices = Indexing(self, self.variables["_sub_idx"])
# Deal with special indices
for key, value in self.source.variables.indices.items():
if value == "0":
self.variables.indices[key] = "0"
elif value == "_idx":
continue # nothing to do, already uses _sub_idx correctly
else:
raise ValueError(
f"Do not know how to deal with variable '{key}' "
f"using index '{value}' in a subgroup."
)
self.namespace = self.source.namespace
self.codeobj_class = self.source.codeobj_class
self._enable_group_attributes()
spikes = property(lambda self: self.source.spikes)
def __getitem__(self, item):
if not isinstance(item, slice):
raise TypeError("Subgroups can only be constructed using slicing syntax")
start, stop, step = item.indices(self._N)
if step != 1:
raise IndexError("Subgroups have to be contiguous")
if start >= stop:
raise IndexError(
f"Illegal start/end values for subgroup, {int(start)}>={int(stop)}"
)
return Subgroup(self.source, self.start + start, self.start + stop)
def __repr__(self):
classname = self.__class__.__name__
return (
f"<{classname} {self.name!r} of {self.source.name!r} "
f"from {self.start} to {self.stop}>"
)