Cell Arrays

Cell Arrays is a Python package that provides a TileDB-backed store for large collections of genomic experimental data, such as millions of cells across multiple single-cell experiment objects.

Install the package

To get started, install the package from PyPI

pip install cellarr

Build the CellArrDataset

The CellArrDataset method is designed to store single-cell RNA-seq datasets but can be generalized to store any 2-dimensional experimental data.

This method creates four TileDB files in the directory specified by output_path:

• gene_annotation: A TileDB file containing feature/gene annotations.

• sample_metadata: A TileDB file containing sample metadata.

• cell_metadata: A TileDB file containing cell metadata including mapping to the samples they are tagged with in sample_metadata.

• A matrix TileDB file named by the layer_matrix_name parameter. This allows the package to store multiple different matrices, e.g. normalized, scaled for the same cell, gene, sample metadata attributes.

The TileDB matrix file is stored in a cell X gene orientation. This orientation is chosen because the fastest-changing dimension as new files are added to the collection is usually the cells rather than genes.

Process:

1. Scan the Collection: Scan the entire collection of files to create a unique set of feature ids (e.g. gene symbols). Store this set as the gene_annotation TileDB file.

2. Sample Metadata: Store sample metadata in sample_metadata TileDB file. Each file is typically considered a sample, and an automatic mapping is created between files and samples.

3. Store Cell Metadata: Store cell metadata in the cell_metadata TileDB file.

4. Remap and Orient Data: For each dataset in the collection, remap and orient the feature dimension using the feature set from Step 1. This step ensures consistency in gene measurement and order, even if some genes are unmeasured or ordered differently in the original experiments.

Note

Check out the reference documentation for modifying the parameters for any of these steps.

First lets mock a few AnnData objects:

import anndata
import numpy as np
import pandas as pd

def generate_adata(n, d, k):
    np.random.seed(1)

    z = np.random.normal(loc=np.arange(k), scale=np.arange(k) * 2, size=(n, k))
    w = np.random.normal(size=(d, k))
    y = np.dot(z, w.T)

    gene_index = [f"gene_{i+1}" for i in range(d)]
    var_df = pd.DataFrame({"names": gene_index}, index=gene_index)
    obs_df = pd.DataFrame({"cells": [f"cell1_{j+1}" for j in range(n)]})

    adata = anndata.AnnData(layers={"counts": y}, var=var_df, obs=obs_df)

    return adata

adata1 = generate_adata(1000, 100, 10)
adata2 = generate_adata(100, 1000, 100)

print("datasets")
print(adata1, adata2)

datasets
AnnData object with n_obs × n_vars = 1000 × 100
    obs: 'cells'
    var: 'names'
    layers: 'counts' AnnData object with n_obs × n_vars = 100 × 1000
    obs: 'cells'
    var: 'names'
    layers: 'counts'

/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/anndata/_core/aligned_df.py:67: ImplicitModificationWarning: Transforming to str index.
  warnings.warn("Transforming to str index.", ImplicitModificationWarning)
/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/anndata/_core/aligned_df.py:67: ImplicitModificationWarning: Transforming to str index.
  warnings.warn("Transforming to str index.", ImplicitModificationWarning)

To build a CellArrDataset from a collection of H5AD or AnnData objects:

import anndata
import numpy as np
import tempfile
from cellarr import build_cellarrdataset, CellArrDataset, MatrixOptions

# Create a temporary directory
tempdir = tempfile.mkdtemp()

# # Read AnnData objects
# adata1 = anndata.read_h5ad("path/to/object1.h5ad", "r")
# # or just provide the path
# adata2 = "path/to/object2.h5ad"

# Build CellArrDataset
dataset = build_cellarrdataset(
    output_path=tempdir,
    files=[adata1, adata2],
    matrix_options=MatrixOptions(dtype=np.float32),
)

print(dataset)

/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/cellarr/build_cellarrdataset.py:217: UserWarning: Scanning all files for feature ids (e.g. gene symbols), this may take long
  warnings.warn(
/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/cellarr/build_cellarrdataset.py:279: UserWarning: Scanning all files to compute cell counts, this may take long
  warnings.warn(
/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/cellarr/build_cellarrdataset.py:286: UserWarning: Sample metadata is not provided, each dataset in 'files' is considered a sample
  warnings.warn(
/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/cellarr/build_cellarrdataset.py:301: UserWarning: Scanning all files for feature ids (e.g. gene symbols), this may take long
  warnings.warn(
/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/cellarr/build_cellarrdataset.py:328: UserWarning: Scanning all files to compute cell counts, this may take long
  warnings.warn(

Optimizing /tmp/tmp2101axqc/gene_annotation
Fragments before consolidation: 1
Fragments after consolidation: 1
Optimizing /tmp/tmp2101axqc/sample_metadata
Fragments before consolidation: 1
Fragments after consolidation: 1
Optimizing /tmp/tmp2101axqc/cell_metadata
Fragments before consolidation: 1
Fragments after consolidation: 1

Optimizing /tmp/tmp2101axqc/counts
Fragments before consolidation: 2

Fragments after consolidation: 1
class: CellArrDataset
number_of_rows: 1100
number_of_columns: 1000
path: '/tmp/tmp2101axqc'

Important

All files are expected to be consistent and any modifications to make them consistent is outside the scope of this function and package.

There’s a few assumptions this process makes:

• If object in files is an AnnData or H5AD object, these must contain an assay matrix in the layers slot of the object named as layer_matrix_name parameter.

• Feature information must contain a column defined by the parameter feature_column in the GeneAnnotationOptions. that contains feature ids or gene symbols across all files.

• If no cell_metadata is provided, we scan to count the number of cells and create a simple range index.

• Each file is considered a sample and a mapping between cells and samples is automatically created. Hence the sample information provided must match the number of input files.

Query a CellArrDataset

Users have the option to reuse the dataset object retuned when building the dataset or by creating a CellArrDataset object by initializing it to the path where the files were created.

# Create a CellArrDataset object from the existing dataset
dataset = CellArrDataset(dataset_path=tempdir)

# Query data from the dataset
expression_data = dataset[10, ["gene_1", "gene_10", "gene_500"]]

print("matrix slice:")
print(expression_data.matrix)

print("\n\n gene_annotation slice:")
print(expression_data.gene_annotation)

print("\n\n cell_metadata slice:")
print(expression_data.cell_metadata)

shape: (1, 3)
matrix slice:
  (0, 0)	12.436595916748047
  (0, 1)	22.075590133666992


 gene_annotation slice:
    cellarr_gene_index
0               gene_1
1              gene_10
447           gene_500


 cell_metadata slice:
   cellarr_sample cellarr_cell_index_in_sample
10       sample_1                           10

This returns a CellArrDatasetSlice object that contains the matrix and metadata DataFrame’s along the cell and gene axes.

Users can easily convert these to analysis-ready representations

print("as anndata:")
print(expression_data.to_anndata())

print("\n\n as summarizedexperiment:")
print(expression_data.to_summarizedexperiment())

as anndata:
AnnData object with n_obs × n_vars = 1 × 3
    obs: 'cellarr_sample', 'cellarr_cell_index_in_sample'
    var: 'cellarr_gene_index'
    layers: 'matrix'


 as summarizedexperiment:
class: SummarizedExperiment
dimensions: (3, 1)
assays(1): ['matrix']
row_data columns(1): ['cellarr_gene_index']
row_names(3): ['0', '1', '447']
column_data columns(2): ['cellarr_sample', 'cellarr_cell_index_in_sample']
column_names(1): ['10']
metadata(0): 

/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/anndata/_core/aligned_df.py:67: ImplicitModificationWarning: Transforming to str index.
  warnings.warn("Transforming to str index.", ImplicitModificationWarning)
/home/runner/work/cellarr/cellarr/.tox/docs/lib/python3.9/site-packages/anndata/_core/aligned_df.py:67: ImplicitModificationWarning: Transforming to str index.
  warnings.warn("Transforming to str index.", ImplicitModificationWarning)

A single cell dataloader

A basic single cell dataloader can be instantiated by using the DataModule class.

from cellarr.dataloader import DataModule

datamodule = DataModule(
    dataset_path="/path/to/cellar/dir",
    cell_metadata_uri="cell_metadata",
    gene_annotation_uri="gene_annotation",
    matrix_uri="counts",
    label_column_name="label",
    study_column_name="study",
    batch_size=1000,
    lognorm=True,
    target_sum=1e4,
)

Users can optionally set a list of studies to be used as validation. If not provided, all studies are used for training. Additionally users may also provide the gene space to train their models.

val_studies = ["study1", "study100"]

gene_list = [
    "GPNMB", "TREM2", "LPL", "HLA-DQA1", "CD109",
    "IL6ST", "SDC2", "MSR1", "ALCAM", "SLC1A3",
    "CD9", "CD59", "MRC1", "SLC11A1", "CPM",
    "GPR183", "ITGAX", "HLA-DMB", "NRP2", "SV2C",
    "PTPRJ", "EMP1", "HLA-DQB1", "MERTK", "CD52",
    "CXCL16", "ABCA1", "HLA-DPB1", "OLR1", "CD83"
]

datamodule = DataModule(
    dataset_path="/path/to/cellar/dir",
    cell_metadata_uri="cell_metadata",
    gene_annotation_uri="gene_annotation",
    matrix_uri="counts",
    val_studies=val_studies,
    label_column_name="label",
    study_column_name="study",
    gene_order=gene_list,
    batch_size=1000,
    lognorm=True,
    target_sum=1e4,
)

Users can access training cells by index.

datamodule.train_dataset[100]

Batches can be created and examined.

dataloader = datamodule.train_dataloader()

batch = next(iter(dataloader))
expression, labels, studies = batch

---

Check out the documentation for more details.