"""Connectivity kernel module."""
from copy import copy
from anndata import AnnData
from cellrank import logging as logg
from cellrank.ul._docs import d
from cellrank.tl.kernels import Kernel
[docs]@d.dedent
class ConnectivityKernel(Kernel):
"""
Kernel which computes transition probabilities based on similarities among cells.
As a measure of similarity, we currently support:
- transcriptomic similarities, computed using e.g. :func:`scanpy.pp.neighbors`, see [Wolf18]_.
- spatial similarities, computed using e.g. :func:`squidpy.gr.spatial_neighbors`, see [Palla21]_.
The resulting transition matrix is symmetric and thus cannot be used to learn about the direction of the biological
process. To include this direction, consider combining with a velocity-derived transition matrix via
:class:`cellrank.tl.kernels.VelocityKernel`.
%(density_correction)s
Parameters
----------
%(adata)s
%(backward)s
conn_key
Key in :attr:`anndata.AnnData.obsp` to obtain the connectivity matrix, describing cell-cell similarity.
%(cond_num)s
check_connectivity
Check whether the underlying KNN graph is connected.
"""
def __init__(
self,
adata: AnnData,
backward: bool = False,
conn_key: str = "connectivities",
compute_cond_num: bool = False,
check_connectivity: bool = False,
):
super().__init__(
adata,
backward=backward,
compute_cond_num=compute_cond_num,
check_connectivity=check_connectivity,
key=conn_key,
)
self._key = conn_key
[docs] def compute_transition_matrix(
self, density_normalize: bool = True
) -> "ConnectivityKernel":
"""
Compute transition matrix based on transcriptomic similarity.
Uses symmetric, weighted KNN graph to compute symmetric transition matrix. The connectivities are computed
using :func:`scanpy.pp.neighbors`. Depending on the parameters used there, they can be UMAP connectivities or
gaussian-kernel-based connectivities with adaptive kernel width.
Parameters
----------
density_normalize
Whether or not to use the underlying KNN graph for density normalization.
Returns
-------
:class:`cellrank.tl.kernels.ConnectivityKernel`
Makes :paramref:`transition_matrix` available.
"""
# fmt: off
start = logg.info(f"Computing transition matrix based on `adata.obsp[{self._key!r}]`")
if self._reuse_cache({"dnorm": density_normalize, "key": self._key}, time=start):
return self
self._compute_transition_matrix(matrix=self._conn.copy(), density_normalize=density_normalize)
logg.info(" Finish", time=start)
# fmt: on
return self
[docs] def copy(self) -> "ConnectivityKernel":
"""Return a copy of self."""
ck = ConnectivityKernel(self.adata, backward=self.backward)
ck._params = copy(self.params)
ck._cond_num = self.condition_number
ck._transition_matrix = copy(self._transition_matrix)
return ck