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Count Matrix Ingestion

Basic CSV/TSV Loading

python
import pandas as pd

# TSV with gene IDs as first column
counts = pd.read_csv('counts.tsv', sep='\t', index_col=0)

# CSV with header
counts = pd.read_csv('counts.csv', index_col=0)

# Skip comment lines
counts = pd.read_csv('counts.txt', sep='\t', index_col=0, comment='#')

featureCounts Output

python
import pandas as pd

# featureCounts format has 6 metadata columns before counts
fc = pd.read_csv('featurecounts.txt', sep='\t', comment='#')
counts = fc.set_index('Geneid').iloc[:, 5:]  # Skip Chr, Start, End, Strand, Length
counts.columns = [c.replace('.bam', '').split('/')[-1] for c in counts.columns]

Salmon Quant Files

python
import pandas as pd
from pathlib import Path

def load_salmon_quants(quant_dirs, column='NumReads'):
    '''Load multiple Salmon quant.sf files into a count matrix.'''
    dfs = {}
    for qdir in quant_dirs:
        sample = Path(qdir).name
        sf = pd.read_csv(f'{qdir}/quant.sf', sep='\t', index_col=0)
        dfs[sample] = sf[column]
    return pd.DataFrame(dfs)

# Usage
quant_dirs = ['salmon_out/sample1', 'salmon_out/sample2', 'salmon_out/sample3']
counts = load_salmon_quants(quant_dirs, column='NumReads')
tpm = load_salmon_quants(quant_dirs, column='TPM')

kallisto Abundance Files

python
import pandas as pd
from pathlib import Path

def load_kallisto_quants(abundance_files, column='est_counts'):
    '''Load multiple kallisto abundance.tsv files.'''
    dfs = {}
    for f in abundance_files:
        sample = Path(f).parent.name
        ab = pd.read_csv(f, sep='\t', index_col=0)
        dfs[sample] = ab[column]
    return pd.DataFrame(dfs)

# Usage
files = ['kallisto_out/sample1/abundance.tsv', 'kallisto_out/sample2/abundance.tsv']
counts = load_kallisto_quants(files, column='est_counts')
tpm = load_kallisto_quants(files, column='tpm')

10X Genomics Sparse Matrix

python
import scanpy as sc

# Load 10X directory (contains matrix.mtx, genes.tsv/features.tsv, barcodes.tsv)
adata = sc.read_10x_mtx('filtered_feature_bc_matrix/')

# Load 10X H5 file
adata = sc.read_10x_h5('filtered_feature_bc_matrix.h5')

# Convert to dense DataFrame if needed
counts = adata.to_df()

AnnData H5AD Files

python
import anndata as ad
import scanpy as sc

# Load h5ad
adata = sc.read_h5ad('data.h5ad')

# Access count matrix
counts = adata.to_df()  # Dense DataFrame
sparse_counts = adata.X  # Sparse matrix (if stored sparse)

# Access raw counts if normalized data is in .X
raw_counts = adata.raw.to_adata().to_df()

RDS Files (from R)

python
import pyreadr

# Read RDS file
result = pyreadr.read_r('counts.rds')
counts = result[None]  # Access the data

# For Seurat objects, use anndata2ri or convert in R first

Combine Multiple Files

python
import pandas as pd
from pathlib import Path

def combine_count_files(file_pattern, index_col=0, sep='\t'):
    '''Combine multiple count files into one matrix.'''
    files = sorted(Path('.').glob(file_pattern))
    dfs = {}
    for f in files:
        sample = f.stem.replace('_counts', '')
        dfs[sample] = pd.read_csv(f, sep=sep, index_col=index_col).iloc[:, 0]
    return pd.DataFrame(dfs)

# Usage
counts = combine_count_files('counts/*_counts.tsv')

Filter Low-Count Genes

python
# Keep genes with at least 10 counts in at least 3 samples
min_counts, min_samples = 10, 3
expressed = (counts >= min_counts).sum(axis=1) >= min_samples
counts_filtered = counts.loc[expressed]

# Alternative: total counts threshold
counts_filtered = counts[counts.sum(axis=1) >= 50]

Handle Gene ID Versions

python
# Remove Ensembl version numbers (ENSG00000123456.12 -> ENSG00000123456)
counts.index = counts.index.str.split('.').str[0]

# Or keep as-is for compatibility

Save Count Matrix

python
# Save as TSV
counts.to_csv('count_matrix.tsv', sep='\t')

# Save as compressed
counts.to_csv('count_matrix.tsv.gz', sep='\t', compression='gzip')

# Save as AnnData
import anndata as ad
adata = ad.AnnData(counts)
adata.write_h5ad('counts.h5ad')

R Loading Equivalents

r
# Basic CSV/TSV
counts <- read.csv('counts.csv', row.names=1)
counts <- read.delim('counts.tsv', row.names=1)

# featureCounts
fc <- read.delim('featurecounts.txt', comment.char='#', row.names=1)
counts <- fc[, 6:ncol(fc)]

# tximport for Salmon/kallisto
library(tximport)
files <- file.path('salmon_out', samples, 'quant.sf')
txi <- tximport(files, type='salmon', txOut=TRUE)
counts <- txi$counts

Related Skills

• rna-quantification/featurecounts-counting - Generate featureCounts output
• rna-quantification/alignment-free-quant - Generate Salmon/kallisto output
• expression-matrix/sparse-handling - Memory-efficient storage
• expression-matrix/gene-id-mapping - Convert gene identifiers

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