Solution
process '6C_ASE_knownSNPs' {
tag "$sampleId"
publishDir "$params.results/$sampleId"
input:
file genome from genome_file
file index from genome_index_ch
file dict from genome_dict_ch
set sampleId, file(vcf), file(bam), file(bai) from grouped_vcf_bam_bai_ch
output:
file "ASE.tsv"
script:
"""
echo "${bam.join('\n')}" > bam.list
java -jar $GATK -R ${genome} \
-T ASEReadCounter \
-o ASE.tsv \
-I bam.list \
-sites ${vcf}
"""
}