Scvelo Agent Skill

import scvelo as scv
import scanpy as sc
import numpy as np
import matplotlib.pyplot as plt

# Configure settings
scv.settings.verbosity = 3       # Show computation steps
scv.settings.presenter_view = True
scv.settings.set_figure_params('scvelo')

# Load data (AnnData with spliced/unspliced layers)
# Option A: Load from loom (velocyto output)
adata = scv.read("cellranger_output.loom", cache=True)

# Option B: Merge velocyto loom with Scanpy-processed AnnData
adata_processed = sc.read_h5ad("processed.h5ad")  # Has UMAP, clusters
adata_velocity = scv.read("velocyto.loom")
adata = scv.utils.merge(adata_processed, adata_velocity)

# Verify layers
print(adata)
# obs × var: N × G
# layers: 'spliced', 'unspliced' (required)
# obsm['X_umap'] (required for visualization)

# Filter and normalize. As of scVelo 0.3, filter_and_normalize() only filters
# genes and normalizes per cell -- it no longer takes n_top_genes and no longer
# log-transforms, so the log step and HVG selection come from Scanpy.
scv.pp.filter_and_normalize(
    adata,
    min_shared_counts=20    # Minimum counts in spliced+unspliced
)
sc.pp.log1p(adata)
sc.pp.highly_variable_genes(adata, n_top_genes=2000, subset=True)

# Compute first and second order moments (means and variances)
# knn_connectivities must be computed first
sc.pp.neighbors(adata, n_neighbors=30, n_pcs=30)
scv.pp.moments(
    adata,
    n_pcs=30,
    n_neighbors=30
)

# Stochastic velocity (faster, less accurate)
scv.tl.velocity(adata, mode='stochastic')
scv.tl.velocity_graph(adata)

# Visualize
scv.pl.velocity_embedding_stream(
    adata,
    basis='umap',
    color='leiden',
    title="RNA Velocity (Stochastic)"
)

# Recover dynamics (computationally intensive; ~10-30 min for 10K cells)
scv.tl.recover_dynamics(adata, n_jobs=4)

# Compute velocity from dynamical model
scv.tl.velocity(adata, mode='dynamical')
scv.tl.velocity_graph(adata)

# Compute latent time
scv.tl.latent_time(adata)

# Visualize latent time on UMAP
scv.pl.scatter(
    adata,
    color='latent_time',
    color_map='gnuplot',
    size=80,
    title='Latent time'
)

# Identify top genes ordered by latent time
top_genes = adata.var['fit_likelihood'].sort_values(ascending=False).index[:300]
scv.pl.heatmap(
    adata,
    var_names=top_genes,
    sortby='latent_time',
    col_color='leiden',
    n_convolve=100
)

# Identify genes with highest velocity fit
scv.tl.rank_velocity_genes(adata, groupby='leiden', min_corr=0.3)
df = scv.DataFrame(adata.uns['rank_velocity_genes']['names'])
print(df.head(10))

# Speed and coherence
scv.tl.velocity_confidence(adata)
scv.pl.scatter(
    adata,
    c=['velocity_length', 'velocity_confidence'],
    cmap='coolwarm',
    perc=[5, 95]
)

# Phase portraits for specific genes
scv.pl.velocity(adata, ['Cpe', 'Gnao1', 'Ins2'],
               ncols=3, figsize=(16, 4))

# Arrow plot on UMAP
scv.pl.velocity_embedding(
    adata,
    arrow_length=3,
    arrow_size=2,
    color='leiden',
    basis='umap'
)

# Stream plot (cleaner visualization)
scv.pl.velocity_embedding_stream(
    adata,
    basis='umap',
    color='leiden',
    smooth=0.8,
    min_mass=4
)

# Velocity pseudotime (alternative to latent time)
scv.tl.velocity_pseudotime(adata)
scv.pl.scatter(adata, color='velocity_pseudotime', cmap='gnuplot')

# PAGA graph with velocity-informed transitions
scv.tl.paga(adata, groups='leiden')
df = scv.get_df(adata, 'paga/transitions_confidence', precision=2).T
df.style.background_gradient(cmap='Blues').format('{:.2g}')

# Plot PAGA with velocity
scv.pl.paga(
    adata,
    basis='umap',
    size=50,
    alpha=0.1,
    min_edge_width=2,
    node_size_scale=1.5
)

import scvelo as scv
import scanpy as sc

def run_rna_velocity(adata, n_top_genes=2000, mode='dynamical', n_jobs=4):
    """
    Complete RNA velocity workflow.

    Args:
        adata: AnnData with 'spliced' and 'unspliced' layers, UMAP in obsm
        n_top_genes: Number of top HVGs for velocity
        mode: 'stochastic' (fast) or 'dynamical' (accurate)
        n_jobs: Parallel jobs for dynamical model

    Returns:
        Processed AnnData with velocity information
    """
    scv.settings.verbosity = 2

    # 1. Preprocessing (scVelo 0.3 dropped log/HVG from filter_and_normalize)
    scv.pp.filter_and_normalize(adata, min_shared_counts=20)
    sc.pp.log1p(adata)
    sc.pp.highly_variable_genes(adata, n_top_genes=n_top_genes, subset=True)

    if 'neighbors' not in adata.uns:
        sc.pp.neighbors(adata, n_neighbors=30)

    scv.pp.moments(adata, n_pcs=30, n_neighbors=30)

    # 2. Velocity estimation
    if mode == 'dynamical':
        scv.tl.recover_dynamics(adata, n_jobs=n_jobs)

    scv.tl.velocity(adata, mode=mode)
    scv.tl.velocity_graph(adata)

    # 3. Downstream analyses
    if mode == 'dynamical':
        scv.tl.latent_time(adata)
        scv.tl.rank_velocity_genes(adata, groupby='leiden', min_corr=0.3)

    scv.tl.velocity_confidence(adata)
    scv.tl.velocity_pseudotime(adata)

    return adata