TRIMMOMATIC PE¶
Trim paired-end reads with trimmomatic. (De)compress with pigz.
Software dependencies¶
- trimmomatic ==0.36
- pigz ==2.3.4
Example¶
This wrapper can be used in the following way:
rule trimmomatic_pe:
input:
r1="reads/{sample}.1.fastq.gz",
r2="reads/{sample}.2.fastq.gz"
output:
r1="trimmed/{sample}.1.fastq.gz",
r2="trimmed/{sample}.2.fastq.gz",
# reads where trimming entirely removed the mate
r1_unpaired="trimmed/{sample}.1.unpaired.fastq.gz",
r2_unpaired="trimmed/{sample}.2.unpaired.fastq.gz"
log:
"logs/trimmomatic/{sample}.log"
params:
# list of trimmers (see manual)
trimmer=["TRAILING:3"],
# optional parameters
extra="",
compression_level="-9"
threads:
32
wrapper:
"0.37.1/bio/trimmomatic/pe"
Note that input, output and log file paths can be chosen freely. When running with
snakemake --use-conda
the software dependencies will be automatically deployed into an isolated environment before execution.
Authors¶
- Johannes Köster
- Jorge Langa
Code¶
"""
bio/trimmomatic/pe
Snakemake wrapper to trim reads with trimmomatic in PE mode with help of pigz.
pigz is the parallel implementation of gz. Trimmomatic spends most of the time
compressing and decompressing instead of trimming sequences. By using process
substitution (<(command), >(command)), we can accelerate trimmomatic a lot.
Consider providing this wrapper with at least 1 extra thread per each gzipped
input or output file.
"""
__author__ = "Johannes Köster, Jorge Langa"
__copyright__ = "Copyright 2016, Johannes Köster"
__email__ = "koester@jimmy.harvard.edu"
__license__ = "MIT"
from snakemake.shell import shell
# Distribute available threads between trimmomatic itself and any potential pigz instances
def distribute_threads(input_files, output_files, available_threads):
gzipped_input_files = sum(1 for file in input_files if file.endswith(".gz"))
gzipped_output_files = sum(1 for file in output_files if file.endswith(".gz"))
potential_threads_per_process = available_threads // (1 + gzipped_input_files + gzipped_output_files)
if potential_threads_per_process > 0:
# decompressing pigz creates at most 4 threads
pigz_input_threads = min(4, potential_threads_per_process) if gzipped_input_files != 0 else 0
pigz_output_threads = \
(available_threads - pigz_input_threads * gzipped_input_files) // (1 + gzipped_output_files) \
if gzipped_output_files != 0 else 0
trimmomatic_threads = available_threads - pigz_input_threads * gzipped_input_files - \
pigz_output_threads * gzipped_output_files
else:
# not enough threads for pigz
pigz_input_threads = 0
pigz_output_threads = 0
trimmomatic_threads = available_threads
return trimmomatic_threads, pigz_input_threads, pigz_output_threads
def compose_input_gz(filename, threads):
if filename.endswith(".gz") and threads > 0:
return "<(pigz -p {threads} --decompress --stdout {filename})".format(
threads=threads,
filename=filename
)
return filename
def compose_output_gz(filename, threads, compression_level):
if filename.endswith(".gz") and threads > 0:
return ">(pigz -p {threads} {compression_level} > {filename})".format(
threads=threads,
compression_level=compression_level,
filename=filename
)
return filename
extra = snakemake.params.get("extra", "")
log = snakemake.log_fmt_shell(stdout=True, stderr=True)
compression_level = snakemake.params.get("compression_level", "-5")
trimmer = " ".join(snakemake.params.trimmer)
# Distribute threads
input_files = [snakemake.input.r1, snakemake.input.r2]
output_files = [snakemake.output.r1, snakemake.output.r1_unpaired,
snakemake.output.r2, snakemake.output.r2_unpaired]
trimmomatic_threads, input_threads, output_threads = distribute_threads(
input_files,
output_files,
snakemake.threads
)
input_r1, input_r2 = [compose_input_gz(filename, input_threads) for filename in input_files]
output_r1, output_r1_unp, output_r2, output_r2_unp = [
compose_output_gz(filename, output_threads, compression_level) for filename in output_files
]
shell(
"trimmomatic PE -threads {trimmomatic_threads} {extra} "
"{input_r1} {input_r2} "
"{output_r1} {output_r1_unp} "
"{output_r2} {output_r2_unp} "
"{trimmer} "
"{log}"
)