Index query¶

kmindex query¶

kmindex query allows to query all sequences in FASTA/Q file (gz/bz2) against all sub-indexes registered into a global index \(G\). For each sequence, the output is a list of either shared \(k\)-mer ratios (presence/absence mode) or abundance classes (abundance mode).

Options

kmindex query v0.5.2

DESCRIPTION
  Query index.

USAGE
  kmindex query -i/--index <STR> -q/--fastx <STR> [-n/--names <STR>] [-z/--zvalue <INT>]
                [-r/--threshold <FLOAT>] [-o/--output <STR>] [-s/--single-query <STR>]
                [-f/--format <STR>] [-b/--batch-size <INT>] [-t/--threads <INT>]
                [-v/--verbose <STR>] [-a/--aggregate] [--fast] [-h/--help] [--version]

OPTIONS
  [global]
    -i --index        - Global index path.
    -n --names        - Sub-indexes to query, comma separated. {all}
    -z --zvalue       - Index s-mers and query (s+z)-mers (findere algorithm). {0}
    -r --threshold    - Shared k-mers threshold. in [0.0, 1.0] {0.0}
    -o --output       - Output directory. {output}
    -q --fastx        - Input fasta/q file (supports gz/bzip2) containing the sequence(s) to query.
    -s --single-query - Query identifier. All sequences are considered as a unique query.
    -f --format       - Output format [json|matrix|json_vec] {json}
    -b --batch-size   - Size of query batches (0≈nb_seq/nb_thread). {0}
    -a --aggregate    - Aggregate results from batches into one file. [⚑]
       --fast         - Keep more pages in cache (see doc for details). [⚑]

  [common]
    -t --threads - Number of threads. {1}
    -h --help    - Show this message and exit. [⚑]
       --version - Show version and exit. [⚑]
    -v --verbose - Verbosity level [debug|info|warning|error]. {info}

--single-query <STR>

All sequences in an input file can be considered a unique query by using --single-query query_name. The output file contains then shared \(k\)-mer ratios between the input file and each indexed sample. This corresponds to the query behavior of kmindex-server (see server-query)

--batch-size <INT>

The number of queries in memory is actually batch-size\(\times\)threads.

Presence/Absence query¶

Main parameters

--index <STR>: Path to global index.
--fastx <STR>: File containing queries.
--names <[STR]>: Sub-indexes to query, comma separated.
--zvalue <INT>: Usually in \([0,6]\), see findere algorithm.
--threshold <FLOAT>: Report only ratios > threshold, in \([0.0,1.0]\).

Example: Querying sequence 1 and 2 from query.fasta against the presence/absence index \(D1\). The kmindex repository offers an examples directory where these commands can be tested.

kmindex query --index ./G --fastx query.fasta --names D1 --zvalue 3 --threshold 0 # (1)!

Several indexes can be queried at the same time by using --names D1,D2,....

The results are shared ratios between queries and each sample indexed in \(D1\). See Output formats.

Output formats¶

JSON (--format json)

{
    "D1": {
        "1": {
            "S1": 1.0,
            "S2": 0.0
        },
        "2": {
            "S1": 1.0,
            "S2": 0.0
        }
    }
}

TSV (--format matrix)

D1     S1   S2
D1:1  1.0  0.0
D1:2  1.0  0.0

Abundance query¶

The query mode is automatically determined by the index type. The values reported in the output files are simply abundance classes instead of shared \(k\)-mer ratios.

About the `z` parameter¶

findere is a query-time technique allowing to reduce the false positive rate of an arbitrary AMQF (as Bloom filters) while reducing the number of lookups to resolve a query. Its scope concerns the indexing of objects that are decomposable into sub-objects, i.e. a sequence of characters. It is based on the following straightforward statement: if a sequence \(S \in E\), then its sub-words \(w_i \in E\).

To benefit from findere, small \(k\)-mers are actually indexed (\(s\)-mer), and (\(s+z\))-mers are considered are query time. As a result, for a given false positive rate of \(\epsilon\), the probability of a false match becomes \(\epsilon^z\) at query time, reducing the false postive rate by several orders of magnitude. Note that \(z\) cannot be arbitrary large, usually \(z \in [0, 6]\), see findere paper for more details.