Add bam filtering on fragment length script

CHANGELOG.md

@@ -32,6 +32,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 * [#512](https://github.com/nf-core/eager/issues/512) Added flexible trimming of bams by library type. 'half' and 'none' UDG libraries can now be trimmed differentially within a single eager run.
 * Added a `.dockstore.yml` config file for automatic workflow registration with [dockstore.org](https://dockstore.org/)
 * Updated template to nf-core/tools 1.10.2
+* [#544](https://github.com/nf-core/eager/pull/544) Add script to perform bam filtering on fragment length
 
 ### `Fixed`
 

bin/filter_bam_fragment_length.py

@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+
+import argparse
+import pysam
+
+
+def get_args():
+    """This function parses and return arguments passed in"""
+    parser = argparse.ArgumentParser(
+        prog="bam_filter", description="Filter bam on fragment length"
+    )
+    parser.add_argument("bam", help="Bam aligment file")
+    parser.add_argument(
+        "-l",
+        dest="fraglen",
+        default=35,
+        type=int,
+        help="Minimum fragment length. Default = 35",
+    )
+    parser.add_argument(
+        "-a",
+        dest="all",
+        default=False,
+        action="store_true",
+        help="Include all reads, even unmapped",
+    )
+    parser.add_argument(
+        "-o",
+        dest="output",
+        default=None,
+        help="Output bam basename. Default = {bam_basename}.filtered.bam",
+    )
+
+    args = parser.parse_args()
+
+    bam = args.bam
+    fraglen = args.fraglen
+    allreads = args.all
+    outfile = args.output
+
+    return (bam, fraglen, allreads, outfile)
+
+
+def getBasename(file_name):
+    if ("/") in file_name:
+        basename = file_name.split("/")[-1].split(".")[0]
+    else:
+        basename = file_name.split(".")[0]
+    return basename
+
+
+def filter_bam(infile, outfile, fraglen, allreads):
+    """Write bam to file
+
+    Args:
+        infile (stream): pysam stream
+        outfile (str): Path to output bam
+        fraglen(int): Minimum fragment length to keep
+        allreads(bool): Apply on all reads, not only mapped
+    """
+    bamfile = pysam.AlignmentFile(infile, "rb")
+    bamwrite = pysam.AlignmentFile(outfile + ".filtered.bam", "wb", template=bamfile)
+
+    for read in bamfile.fetch(until_eof=True):
+        if allreads:
+            if read.query_length >= fraglen:
+                bamwrite.write(read)
+        else:
+            if read.is_unmapped == False and read.query_length >= fraglen:
+                bamwrite.write(read)
+
+
+if __name__ == "__main__":
+    BAM, FRAGLEN, ALLREADS, OUTFILE = get_args()
+
+    BAMFILE = pysam.AlignmentFile(BAM, "rb")
+
+    if OUTFILE is None:
+        OUTFILE = getBasename(BAM)
+
+    filter_bam(BAM, OUTFILE, FRAGLEN, ALLREADS)
+