Improve the arboreto skill

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Timothy Kassis
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# GRN Inference Algorithms
Arboreto provides two algorithms for gene regulatory network (GRN) inference, both based on the multiple regression approach.
## Algorithm Overview
Both algorithms follow the same inference strategy:
1. For each target gene in the dataset, train a regression model
2. Identify the most important features (potential regulators) from the model
3. Emit these features as candidate regulators with importance scores
The key difference is **computational efficiency** and the underlying regression method.
## GRNBoost2 (Recommended)
**Purpose**: Fast GRN inference for large-scale datasets using gradient boosting.
### When to Use
- **Large datasets**: Tens of thousands of observations (e.g., single-cell RNA-seq)
- **Time-constrained analysis**: Need faster results than GENIE3
- **Default choice**: GRNBoost2 is the flagship algorithm and recommended for most use cases
### Technical Details
- **Method**: Stochastic gradient boosting with early-stopping regularization
- **Performance**: Significantly faster than GENIE3 on large datasets
- **Output**: Same format as GENIE3 (TF-target-importance triplets)
### Usage
```python
from arboreto.algo import grnboost2
network = grnboost2(
expression_data=expression_matrix,
tf_names=tf_names,
seed=42 # For reproducibility
)
```
### Parameters
```python
grnboost2(
expression_data, # Required: pandas DataFrame or numpy array
gene_names=None, # Required for numpy arrays
tf_names='all', # List of TF names or 'all'
verbose=False, # Print progress messages
client_or_address='local', # Dask client or scheduler address
seed=None # Random seed for reproducibility
)
```
## GENIE3
**Purpose**: Classic Random Forest-based GRN inference, serving as the conceptual blueprint.
### When to Use
- **Smaller datasets**: When dataset size allows for longer computation
- **Comparison studies**: When comparing with published GENIE3 results
- **Validation**: To validate GRNBoost2 results
### Technical Details
- **Method**: Random Forest or ExtraTrees regression
- **Foundation**: Original multiple regression GRN inference strategy
- **Trade-off**: More computationally expensive but well-established
### Usage
```python
from arboreto.algo import genie3
network = genie3(
expression_data=expression_matrix,
tf_names=tf_names,
seed=42
)
```
### Parameters
```python
genie3(
expression_data, # Required: pandas DataFrame or numpy array
gene_names=None, # Required for numpy arrays
tf_names='all', # List of TF names or 'all'
verbose=False, # Print progress messages
client_or_address='local', # Dask client or scheduler address
seed=None # Random seed for reproducibility
)
```
## Algorithm Comparison
| Feature | GRNBoost2 | GENIE3 |
|---------|-----------|--------|
| **Speed** | Fast (optimized for large data) | Slower |
| **Method** | Gradient boosting | Random Forest |
| **Best for** | Large-scale data (10k+ observations) | Small-medium datasets |
| **Output format** | Same | Same |
| **Inference strategy** | Multiple regression | Multiple regression |
| **Recommended** | Yes (default choice) | For comparison/validation |
## Advanced: Custom Regressor Parameters
For advanced users, pass custom scikit-learn regressor parameters:
```python
from sklearn.ensemble import GradientBoostingRegressor, RandomForestRegressor
# Custom GRNBoost2 parameters
custom_grnboost2 = grnboost2(
expression_data=expression_matrix,
regressor_type='GBM',
regressor_kwargs={
'n_estimators': 100,
'max_depth': 5,
'learning_rate': 0.1
}
)
# Custom GENIE3 parameters
custom_genie3 = genie3(
expression_data=expression_matrix,
regressor_type='RF',
regressor_kwargs={
'n_estimators': 1000,
'max_features': 'sqrt'
}
)
```
## Choosing the Right Algorithm
**Decision guide**:
1. **Start with GRNBoost2** - It's faster and handles large datasets better
2. **Use GENIE3 if**:
- Comparing with existing GENIE3 publications
- Dataset is small-medium sized
- Validating GRNBoost2 results
Both algorithms produce comparable regulatory networks with the same output format, making them interchangeable for most analyses.

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# Arboreto API Reference
This document provides comprehensive API documentation for the arboreto package, a Python library for gene regulatory network (GRN) inference.
## Overview
Arboreto enables inference of gene regulatory networks from expression data using machine learning algorithms. It supports distributed computing via Dask for scalability from single machines to multi-node clusters.
**Current Version:** 0.1.5
**GitHub:** https://github.com/tmoerman/arboreto
**License:** BSD 3-Clause
## Core Algorithms
### GRNBoost2
The flagship algorithm for fast gene regulatory network inference using stochastic gradient boosting.
**Function:** `arboreto.algo.grnboost2()`
**Parameters:**
- `expression_data` (pandas.DataFrame or numpy.ndarray): Expression matrix where rows are observations (cells/samples) and columns are genes. Required.
- `gene_names` (list, optional): List of gene names matching column order. If None, uses DataFrame column names.
- `tf_names` (list, optional): List of transcription factor names to consider as regulators. If None, all genes are considered potential regulators.
- `seed` (int, optional): Random seed for reproducibility. Recommended when consistent results are needed across runs.
- `client_or_address` (dask.distributed.Client or str, optional): Custom Dask client or scheduler address for distributed computing. If None, creates a default local client.
- `verbose` (bool, optional): Enable verbose output for debugging.
**Returns:**
- pandas.DataFrame with columns `['TF', 'target', 'importance']` representing inferred regulatory links. Each row represents a regulatory relationship with an importance score.
**Algorithm Details:**
- Uses stochastic gradient boosting with early-stopping regularization
- Much faster than GENIE3, especially for large datasets (tens of thousands of observations)
- Extracts important features from trained regression models to identify regulatory relationships
- Recommended as the default choice for most use cases
**Example:**
```python
from arboreto.algo import grnboost2
import pandas as pd
# Load expression data
expression_matrix = pd.read_csv('expression_data.tsv', sep='\t')
tf_list = ['TF1', 'TF2', 'TF3'] # Optional: specify TFs
# Run inference
network = grnboost2(
expression_data=expression_matrix,
tf_names=tf_list,
seed=42 # For reproducibility
)
# Save results
network.to_csv('output_network.tsv', sep='\t', index=False)
```
### GENIE3
Classical gene regulatory network inference using Random Forest regression.
**Function:** `arboreto.algo.genie3()`
**Parameters:**
Same as GRNBoost2 (see above).
**Returns:**
Same format as GRNBoost2 (see above).
**Algorithm Details:**
- Uses Random Forest or ExtraTrees regression models
- Blueprint for multiple regression GRN inference strategy
- More computationally expensive than GRNBoost2
- Better suited for smaller datasets or when maximum accuracy is needed
**When to Use GENIE3 vs GRNBoost2:**
- **Use GRNBoost2:** For large datasets, faster results, or when computational resources are limited
- **Use GENIE3:** For smaller datasets, when following established protocols, or for comparison with published results
## Module Structure
### arboreto.algo
Primary module for typical users. Contains high-level inference functions.
**Main Functions:**
- `grnboost2()` - Fast GRN inference using gradient boosting
- `genie3()` - Classical GRN inference using Random Forest
### arboreto.core
Advanced module for power users. Contains low-level framework components for custom implementations.
**Use cases:**
- Custom inference pipelines
- Algorithm modifications
- Performance tuning
### arboreto.utils
Utility functions for common data processing tasks.
**Key Functions:**
- `load_tf_names(filename)` - Load transcription factor names from file
- Reads a text file with one TF name per line
- Returns a list of TF names
- Example: `tf_names = load_tf_names('transcription_factors.txt')`
## Data Format Requirements
### Input Format
**Expression Matrix:**
- **Format:** pandas DataFrame or numpy ndarray
- **Orientation:** Rows = observations (cells/samples), Columns = genes
- **Convention:** Follows scikit-learn format
- **Gene Names:** Column names (DataFrame) or separate `gene_names` parameter
- **Data Type:** Numeric (float or int)
**Common Mistake:** If data is transposed (genes as rows), use pandas to transpose:
```python
expression_df = pd.read_csv('data.tsv', sep='\t', index_col=0).T
```
**Transcription Factor List:**
- **Format:** Python list of strings or text file (one TF per line)
- **Optional:** If not provided, all genes are considered potential regulators
- **Example:** `['Sox2', 'Oct4', 'Nanog']`
### Output Format
**Network DataFrame:**
- **Columns:**
- `TF` (str): Transcription factor (regulator) gene name
- `target` (str): Target gene name
- `importance` (float): Importance score of the regulatory relationship
- **Interpretation:** Higher importance scores indicate stronger predicted regulatory relationships
- **Sorting:** Typically sorted by importance (descending) for prioritization
**Example Output:**
```
TF target importance
Sox2 Gene1 15.234
Oct4 Gene1 12.456
Sox2 Gene2 8.901
```
## Distributed Computing with Dask
### Local Execution (Default)
Arboreto automatically creates a local Dask client if none is provided:
```python
network = grnboost2(expression_data=expr_matrix, tf_names=tf_list)
```
### Custom Local Cluster
For better control over resources or multiple inferences:
```python
from dask.distributed import Client, LocalCluster
# Configure cluster
cluster = LocalCluster(
n_workers=4,
threads_per_worker=2,
memory_limit='4GB'
)
client = Client(cluster)
# Run inference
network = grnboost2(
expression_data=expr_matrix,
tf_names=tf_list,
client_or_address=client
)
# Clean up
client.close()
cluster.close()
```
### Distributed Cluster
For multi-node computation:
**On scheduler node:**
```bash
dask-scheduler --no-bokeh # Use --no-bokeh to avoid Bokeh errors
```
**On worker nodes:**
```bash
dask-worker scheduler-address:8786 --local-dir /tmp
```
**In Python script:**
```python
from dask.distributed import Client
client = Client('scheduler-address:8786')
network = grnboost2(
expression_data=expr_matrix,
tf_names=tf_list,
client_or_address=client
)
```
### Dask Dashboard
Monitor computation progress via the Dask dashboard:
```python
from dask.distributed import Client, LocalCluster
cluster = LocalCluster(diagnostics_port=8787)
client = Client(cluster)
# Dashboard available at: http://localhost:8787
```
## Reproducibility
To ensure reproducible results across runs:
```python
network = grnboost2(
expression_data=expr_matrix,
tf_names=tf_list,
seed=42 # Fixed seed ensures identical results
)
```
**Note:** Without a seed parameter, results may vary slightly between runs due to randomness in the algorithms.
## Performance Considerations
### Memory Management
- Expression matrices should fit in memory (RAM)
- For very large datasets, consider:
- Using a machine with more RAM
- Distributing across multiple nodes
- Preprocessing to reduce dimensionality
### Worker Configuration
- **Local execution:** Number of workers = number of CPU cores (default)
- **Custom cluster:** Balance workers and threads based on available resources
- **Distributed execution:** Ensure adequate `local_dir` space on worker nodes
### Algorithm Choice
- **GRNBoost2:** ~10-100x faster than GENIE3 for large datasets
- **GENIE3:** More established but slower, better for small datasets (<10k observations)
## Integration with pySCENIC
Arboreto is a core component of the pySCENIC pipeline for single-cell RNA sequencing analysis:
1. **GRN Inference (Arboreto):** Infer regulatory networks using GRNBoost2
2. **Regulon Prediction:** Prune network and identify regulons
3. **Cell Type Identification:** Score regulons across cells
For pySCENIC workflows, arboreto is typically used in the first step to generate the initial regulatory network.
## Common Issues and Solutions
See the main SKILL.md for troubleshooting guidance.

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# Basic GRN Inference with Arboreto
## Input Data Requirements
Arboreto requires gene expression data in one of two formats:
### Pandas DataFrame (Recommended)
- **Rows**: Observations (cells, samples, conditions)
- **Columns**: Genes (with gene names as column headers)
- **Format**: Numeric expression values
Example:
```python
import pandas as pd
# Load expression matrix with genes as columns
expression_matrix = pd.read_csv('expression_data.tsv', sep='\t')
# Columns: ['gene1', 'gene2', 'gene3', ...]
# Rows: observation data
```
### NumPy Array
- **Shape**: (observations, genes)
- **Requirement**: Separately provide gene names list matching column order
Example:
```python
import numpy as np
expression_matrix = np.genfromtxt('expression_data.tsv', delimiter='\t', skip_header=1)
with open('expression_data.tsv') as f:
gene_names = [gene.strip() for gene in f.readline().split('\t')]
assert expression_matrix.shape[1] == len(gene_names)
```
## Transcription Factors (TFs)
Optionally provide a list of transcription factor names to restrict regulatory inference:
```python
from arboreto.utils import load_tf_names
# Load from file (one TF per line)
tf_names = load_tf_names('transcription_factors.txt')
# Or define directly
tf_names = ['TF1', 'TF2', 'TF3']
```
If not provided, all genes are considered potential regulators.
## Basic Inference Workflow
### Using Pandas DataFrame
```python
import pandas as pd
from arboreto.utils import load_tf_names
from arboreto.algo import grnboost2
if __name__ == '__main__':
# Load expression data
expression_matrix = pd.read_csv('expression_data.tsv', sep='\t')
# Load transcription factors (optional)
tf_names = load_tf_names('tf_list.txt')
# Run GRN inference
network = grnboost2(
expression_data=expression_matrix,
tf_names=tf_names # Optional
)
# Save results
network.to_csv('network_output.tsv', sep='\t', index=False, header=False)
```
**Critical**: The `if __name__ == '__main__':` guard is required because Dask spawns new processes internally.
### Using NumPy Array
```python
import numpy as np
from arboreto.algo import grnboost2
if __name__ == '__main__':
# Load expression matrix
expression_matrix = np.genfromtxt('expression_data.tsv', delimiter='\t', skip_header=1)
# Extract gene names from header
with open('expression_data.tsv') as f:
gene_names = [gene.strip() for gene in f.readline().split('\t')]
# Verify dimensions match
assert expression_matrix.shape[1] == len(gene_names)
# Run inference with explicit gene names
network = grnboost2(
expression_data=expression_matrix,
gene_names=gene_names,
tf_names=tf_names
)
network.to_csv('network_output.tsv', sep='\t', index=False, header=False)
```
## Output Format
Arboreto returns a Pandas DataFrame with three columns:
| Column | Description |
|--------|-------------|
| `TF` | Transcription factor (regulator) gene name |
| `target` | Target gene name |
| `importance` | Regulatory importance score (higher = stronger regulation) |
Example output:
```
TF1 gene5 0.856
TF2 gene12 0.743
TF1 gene8 0.621
```
## Setting Random Seed
For reproducible results, provide a seed parameter:
```python
network = grnboost2(
expression_data=expression_matrix,
tf_names=tf_names,
seed=777
)
```
## Algorithm Selection
Use `grnboost2()` for most cases (faster, handles large datasets):
```python
from arboreto.algo import grnboost2
network = grnboost2(expression_data=expression_matrix)
```
Use `genie3()` for comparison or specific requirements:
```python
from arboreto.algo import genie3
network = genie3(expression_data=expression_matrix)
```
See `references/algorithms.md` for detailed algorithm comparison.

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# Distributed Computing with Arboreto
Arboreto leverages Dask for parallelized computation, enabling efficient GRN inference from single-machine multi-core processing to multi-node cluster environments.
## Computation Architecture
GRN inference is inherently parallelizable:
- Each target gene's regression model can be trained independently
- Arboreto represents computation as a Dask task graph
- Tasks are distributed across available computational resources
## Local Multi-Core Processing (Default)
By default, arboreto uses all available CPU cores on the local machine:
```python
from arboreto.algo import grnboost2
# Automatically uses all local cores
network = grnboost2(expression_data=expression_matrix, tf_names=tf_names)
```
This is sufficient for most use cases and requires no additional configuration.
## Custom Local Dask Client
For fine-grained control over local resources, create a custom Dask client:
```python
from distributed import LocalCluster, Client
from arboreto.algo import grnboost2
if __name__ == '__main__':
# Configure local cluster
local_cluster = LocalCluster(
n_workers=10, # Number of worker processes
threads_per_worker=1, # Threads per worker
memory_limit='8GB' # Memory limit per worker
)
# Create client
custom_client = Client(local_cluster)
# Run inference with custom client
network = grnboost2(
expression_data=expression_matrix,
tf_names=tf_names,
client_or_address=custom_client
)
# Clean up
custom_client.close()
local_cluster.close()
```
### Benefits of Custom Client
- **Resource control**: Limit CPU and memory usage
- **Multiple runs**: Reuse same client for different parameter sets
- **Monitoring**: Access Dask dashboard for performance insights
## Multiple Inference Runs with Same Client
Reuse a single Dask client for multiple inference runs with different parameters:
```python
from distributed import LocalCluster, Client
from arboreto.algo import grnboost2
if __name__ == '__main__':
# Initialize client once
local_cluster = LocalCluster(n_workers=8, threads_per_worker=1)
client = Client(local_cluster)
# Run multiple inferences
network_seed1 = grnboost2(
expression_data=expression_matrix,
tf_names=tf_names,
client_or_address=client,
seed=666
)
network_seed2 = grnboost2(
expression_data=expression_matrix,
tf_names=tf_names,
client_or_address=client,
seed=777
)
# Different algorithms with same client
from arboreto.algo import genie3
network_genie3 = genie3(
expression_data=expression_matrix,
tf_names=tf_names,
client_or_address=client
)
# Clean up once
client.close()
local_cluster.close()
```
## Distributed Cluster Computing
For very large datasets, connect to a remote Dask distributed scheduler running on a cluster:
### Step 1: Set Up Dask Scheduler (on cluster head node)
```bash
dask-scheduler
# Output: Scheduler at tcp://10.118.224.134:8786
```
### Step 2: Start Dask Workers (on cluster compute nodes)
```bash
dask-worker tcp://10.118.224.134:8786
```
### Step 3: Connect from Client
```python
from distributed import Client
from arboreto.algo import grnboost2
if __name__ == '__main__':
# Connect to remote scheduler
scheduler_address = 'tcp://10.118.224.134:8786'
cluster_client = Client(scheduler_address)
# Run inference on cluster
network = grnboost2(
expression_data=expression_matrix,
tf_names=tf_names,
client_or_address=cluster_client
)
cluster_client.close()
```
### Cluster Configuration Best Practices
**Worker configuration**:
```bash
dask-worker tcp://scheduler:8786 \
--nprocs 4 \ # Number of processes per node
--nthreads 1 \ # Threads per process
--memory-limit 16GB # Memory per process
```
**For large-scale inference**:
- Use more workers with moderate memory rather than fewer workers with large memory
- Set `threads_per_worker=1` to avoid GIL contention in scikit-learn
- Monitor memory usage to prevent workers from being killed
## Monitoring and Debugging
### Dask Dashboard
Access the Dask dashboard for real-time monitoring:
```python
from distributed import Client
client = Client() # Prints dashboard URL
# Dashboard available at: http://localhost:8787/status
```
The dashboard shows:
- **Task progress**: Number of tasks completed/pending
- **Resource usage**: CPU, memory per worker
- **Task stream**: Real-time visualization of computation
- **Performance**: Bottleneck identification
### Verbose Output
Enable verbose logging to track inference progress:
```python
network = grnboost2(
expression_data=expression_matrix,
tf_names=tf_names,
verbose=True
)
```
## Performance Optimization Tips
### 1. Data Format
- **Use Pandas DataFrame when possible**: More efficient than NumPy for Dask operations
- **Reduce data size**: Filter low-variance genes before inference
### 2. Worker Configuration
- **CPU-bound tasks**: Set `threads_per_worker=1`, increase `n_workers`
- **Memory-bound tasks**: Increase `memory_limit` per worker
### 3. Cluster Setup
- **Network**: Ensure high-bandwidth, low-latency network between nodes
- **Storage**: Use shared filesystem or object storage for large datasets
- **Scheduling**: Allocate dedicated nodes to avoid resource contention
### 4. Transcription Factor Filtering
- **Limit TF list**: Providing specific TF names reduces computation
```python
# Full search (slow)
network = grnboost2(expression_data=matrix)
# Filtered search (faster)
network = grnboost2(expression_data=matrix, tf_names=known_tfs)
```
## Example: Large-Scale Single-Cell Analysis
Complete workflow for processing single-cell RNA-seq data on a cluster:
```python
from distributed import Client
from arboreto.algo import grnboost2
import pandas as pd
if __name__ == '__main__':
# Connect to cluster
client = Client('tcp://cluster-scheduler:8786')
# Load large single-cell dataset (50,000 cells x 20,000 genes)
expression_data = pd.read_csv('scrnaseq_data.tsv', sep='\t')
# Load cell-type-specific TFs
tf_names = pd.read_csv('tf_list.txt', header=None)[0].tolist()
# Run distributed inference
network = grnboost2(
expression_data=expression_data,
tf_names=tf_names,
client_or_address=client,
verbose=True,
seed=42
)
# Save results
network.to_csv('grn_results.tsv', sep='\t', index=False)
client.close()
```
This approach enables analysis of datasets that would be impractical on a single machine.