### Navigation

- index
- modules |
- SamSifter 0.5.5 documentation »
- Module code »

# Source code for samsifter.tools.filter_read_conservation

    #!/usr/bin/env python3
    # -*- coding: utf-8 -*-
    """Filters highly conserved reads in a SAM file.

    Identifies reads assigned to multiple taxa with similar identity. Excludes
    reads mapping to different accessions/taxa with similar alignment scores.

    .. moduleauthor:: Florian Aldehoff <faldehoff@student.uni-tuebingen.de>
    """

    import sys
    if not (sys.version_info[0] >= 3):
        print("Error, I need python 3.x or newer")
        exit(1)

    import argparse
    import logging as log
    import fileinput
    import tempfile
    from os.path import basename, splitext

    """ custom libraries """
    from samsifter.models.filter import FilterItem
    from samsifter.models.parameter import (
        FilterParameter, FilterSwitch, FilterThreshold
    )
    from samsifter.util.arg_sanitation import (check_sam, check_pos_int)
    from samsifter.util.filters import line_filter
    from samsifter.util.papertrail import modify_header
    from samsifter.version import samsifter_version

    __version__ = samsifter_version

    """ global variables """
    TEXT = "Filter reads by conservation"
    DESC = ("Filters reads assigned to multiple taxa with similar identity. "
            "Excludes reads mapping to different accessions/taxa with similar "
            "alignment scores.")

    def item():
        """Create FilterItem for this filter to be used in list and tree models.

        Returns
        -------
        FilterItem
            Object representing this filter in item-based models.
        """
        item = FilterItem(text=TEXT, desc=DESC)
        item.set_command(splitext(basename(__file__))[0])

        item.add_parameter(FilterThreshold(
            text="AS deviation",
            desc="permitted deviation from max alignment score [5]",
            cli_name="--as_dev",
            default=5,
            minimum=1,
            precision=0,
            required=True
        ))

        item.add_parameter(FilterThreshold(
            text="max. taxa",
            desc="maximum number of taxa [10]",
            cli_name="--max_taxa",
            default=10,
            minimum=1,
            precision=0,
            required=True
        ))

        item.add_parameter(FilterSwitch(
            text="filter direction",
            desc="Keep or discard entries passing the filter criteria?",
            cli_name="--discard",
            default=0,
            options=["discard", "keep"]
        ))

        item.add_parameter(FilterParameter(
            text="verbose",
            desc="print additional information to STDERR",
            cli_name="--verbose",
            default=True,
            active=True
        ))

        item.add_parameter(FilterParameter(
            text="debug",
            desc="print debug messages to STDERR",
            cli_name="--debug",
            default=False
        ))

        item.add_parameter(FilterParameter(
            text="write PG tag",
            desc="annotate the filtered SAM file by adding a PG tag to the header",
            cli_name="--modify",
            default=True,
            active=True
        ))

        return item

    def main():
        """Executable to filter SAM files for reads with high conservation.

        See ``--help`` for details on expected arguments. Takes input from
        either STDIN, or optional, or positional arguments. Logs messages to
        STDERR and writes processed SAM files to STDOUT.
        """
        # parse arguments
        parser = argparse.ArgumentParser(description=DESC)
        parser.add_argument('-i', '--input',
                            type=check_sam,
                            help="specify SAM file to be analysed (default: "
                            "STDIN)",
                            required=False)
        parser.add_argument('--discard',
                            type=int,
                            help="keep or discard entries passing the filter "
                                 "criteria?",
                            required=False,
                            default=0)
        parser.add_argument('-v', '--verbose',
                            required=False,
                            action='store_true',
                            help='print additional information to stderr')
        parser.add_argument('-d', '--debug',
                            required=False,
                            action='store_true',
                            help='print debug messages to stderr')
        parser.add_argument('-m', '--modify',
                            required=False,
                            action='store_true',
                            help='modify header by adding PG record')
        parser.add_argument("--as_dev",
                            action="store",
                            type=check_pos_int,
                            dest="as_dev",
                            help=("permitted deviation from max alignment score "
                                  "[5]"),
                            default=5)
        parser.add_argument("--max_taxa",
                            action="store",
                            type=check_pos_int,
                            dest="max_taxa",
                            help="maximum number of taxa [10]",
                            default=10)

        (args, remainArgs) = parser.parse_known_args()

        # configure logging
        if args.verbose:
            log.basicConfig(format="%(levelname)s: %(message)s", level=log.DEBUG)
        else:
            log.basicConfig(format="%(levelname)s: %(message)s")

        # initialize dicts and variables
        header = []      # SAM header lines, unmodified
        queries = {}     # dict of dicts of lists: query -> score -> taxa
        positions = {}   # dict of list for QNAMES and their line numbers
        buffer = None    # file handle used to buffer complete STDIN
        byte_offset = 0  # offset of first line after end of header
        line_offset = 0

        log.info("START of filtering reads by conservation.")

        # parse SAM file
        log.info("STEP 1: parsing SAM records.")
        try:
            """
            open SAM file from either command line argument or STDIN
            use temporary file as buffer if reading from STDIN
            """
            if args.input:
                handle = open(args.input, 'r')
            else:
                handle = fileinput.input(remainArgs)
                buffer = tempfile.TemporaryFile(mode='w+')

            for line_nr, line in enumerate(handle, 0):
                if buffer is not None:
                    buffer.write(line)

                # assuming that headers always precede alignments (SAMv1)
                if line.startswith("@"):
                    if args.modify:
                        line_offset = line_nr + 1
                        # store header lines for later modification
                        header.append(line)
                        # increase offset until reaching end of header
                        byte_offset += len(line)
                else:
                    fields = line.split("\t")
                    """
                    #   content     description
                    ===========================
                    0   QNAME
                    1   FLAG
                    2   RNAME
                    3   POS
                    4   MAPQ
                    5   CIGAR
                    6   RNEXT
                    7   PNEXT
                    8   TLEN
                    9   SEQ
                    10  QUAL
                    ...optional fields...
                    11  AS          alignment score
                    12  NM          edit distance to reference
                    13  ZL          reference length
                    14  ZR          "raw score"
                    15  ZE          "expected"
                    16  ZI          percent identify (incl. indels & deaminated)
                    17  MD          mismatching positions
                    18  NS          PMD score
                    """

                    if len(fields) < 10:
                        continue

                    # extract accession from required RNAME field
                    # (as written by MALT 0.0.3)
                    rname_parts = fields[2].split("|")
                    """
                    #   content
                    ===============
                    0   gi
                    1   GenBank ID
                    2   ref
                    3   accession
                    4   tax
                    5   taxonomy ID
                    """

                    try:
                        taxon_id = rname_parts[5]
                    except IndexError:
                        taxon_id = "unknown"
                        log.warn("no taxon ID in line %i, assigning read to taxon "
                                 "'unknown'" % (line_nr + 1))

                    try:
                        aln_score = int(
                            line.split('AS:i:')[1].split()[0].rstrip('\n')
                        )
                    except IndexError:
                        log.error("no AS tag in line %i" % (line_nr + 1))
                        exit(1)

                    qname = fields[0]
                    if qname in queries:
                        try:
                            # new taxon entry
                            queries[qname][aln_score].append(taxon_id)
                        except KeyError:
                            # new score entry
                            queries[qname][aln_score] = [taxon_id, ]
                    else:
                        # new query entry
                        queries[qname] = {aln_score: [taxon_id, ]}

                    # remember occurence of qname and line number(s)
                    try:
                        positions[qname].append(int(line_nr))
                    except KeyError:
                        positions[qname] = [int(line_nr), ]

        finally:
            handle.close()
            buffer.seek(0)

        # determine query names w/ high-scoring hits in several taxa
        log.info("STEP 2: determining query names matching the filter criteria.")
        lines = []
        for queryname in queries:
            score_dict = queries[queryname]

            # upper and lower bound
            max_score = max(score_dict.keys())
            if args.debug:
                log.info(
                    "max_score: %s of type %s\targs.as_dev: %s of type %s"
                    % (max_score, type(max_score), args.as_dev, type(args.as_dev))
                )
            low_bound = max_score - args.as_dev
            if low_bound < 0:
                low_bound = 0

            # compile list of taxa from the top
            taxon_list = []
            for score in range(low_bound, max_score + 1):
                try:
                    taxon_list += score_dict[score]
                except KeyError:
                    # some scores in range may be missing
                    pass

            if len(set(taxon_list)) > args.max_taxa:
                lines.extend(positions[queryname])
                if args.debug:
                    log.info("filtering query name: %s" % queryname)

        # re-open file if not a buffered stream
        if buffer is None:
            buffer = open(args.input, 'r')

        # skip original headers and sneak in modified headers instead
        if args.modify:
            log.info("Writing new @PG record to SAM header.")
            cl = " ".join(sys.argv[1:])
            modified_header = modify_header(
                header,
                name=splitext(basename(__file__))[0],
                version=__version__,
                command_line=cl,
                description=TEXT
            )
            extra_headers = len(modified_header) - len(header)    # should be 1
            for record in modified_header:
                print(record.rstrip(), file=sys.stdout)
            # fast forward buffer to beginning of alignments
            buffer.seek(byte_offset)

            if args.debug:
                log.info("%i new line added to header lines." % extra_headers)

        # keep or remove query names from SAM file
        alt = ["discarding", "keeping"]
        log.info("STEP 3: %s %i conserved reads from SAM file." %
                 (alt[args.discard], len(lines)))

        line_filter(lines, buffer, discard=(args.discard == 0),
                    offset=line_offset)
        buffer.close()

        log.info("END of filtering reads by conservation.")

        exit()

    if __name__ == "__main__":
        main()

### Navigation

- index
- modules |
- SamSifter 0.5.5 documentation »
- Module code »