sourmash sketch
documentation¶
Most of the commands in sourmash work with signatures, which contain information about genomic or proteomic sequences. Each signature contains one or more sketches, which are compressed versions of these sequences. Using sourmash, you can search, compare, and analyze these sequences in various ways.
To create a signature with one or more sketches, you use the sourmash sketch
command. There are three main commands:
sourmash sketch dna
sourmash sketch protein
sourmash sketch translate
sourmash sketch fromfile
The sketch dna
command reads in DNA sequences and outputs DNA sketches.
The sketch protein
command reads in protein sequences and outputs protein sketches.
The sketch translate
command reads in DNA sequences, translates them in all six frames, and outputs protein sketches.
The sketch fromfile
command takes in a CSV file containing the
locations of genomes and proteomes, and outputs all of the requested
sketches. It is primarily intended for large-scale database construction.
(fromfile
is a new command as of sourmash v4.4.0.)
All sourmash sketch
commands take FASTA or FASTQ sequences as input;
input data can be uncompressed, compressed with gzip, or compressed
with bzip2. The output will be one or more signature files that
can be used by other sourmash commands.
Quickstart¶
DNA sketches for genomes and reads¶
To create a DNA sketch for a genome, run:
sourmash sketch dna genome.fna
This will create an output file genome.fna.sig
in the current directory, containing a single DNA signature for the entire genome, calculated using the default parameters.
Sourmash can work with unassembled reads; run
sourmash sketch dna -p k=21,k=31,k=51,abund metagenome.fq.gz
to create three abundance-weighted sketches at k=21, 31, and 51, for the given FASTQ file.
By default, sketch dna
ignores bad k-mers (e.g. non-ACGT characters
in DNA). If --check-sequence
is provided, sketch dna
will error
exit on the first bad k-mer.
Building a combined sketch from two or more files¶
If you have multiple files, sourmash will by default create one sketch for each file. For situations such as paired-end read files from Illumina sequencing, you may instead want to build a combined sketch.
You can build a combined sketch in two ways.
First, you can use --name/--merge
to build
a single (named) sketch out of multiple input files:
sourmash sketch dna -p k=31 sample_R1.fq.gz sample_R2.fq.gz \
--name "sample" -o sample.zip
Here you need to specify a name because sourmash does not pick a default name when given multiple files; you also need to provide an output file name because sourmash doesn’t pick a default output name in this situation.
Second, you can stream the input files into sourmash sketch
via stdin:
gunzip -c sample_R?.fq.gz | sourmash sketch dna -p k=31 - \
-o sample.zip
As above, you need to specify an output filename because sourmash
can’t guess a good default for streaming input. The --name
option
can still be specified if you want to name the output sketch something
other than -
.
Note that the order of sequences or sequence files does not affect
the output of sourmash sketch
at all: you do not need to
interleave reads or provide the input files in a consistent order.
Protein sketches for genomes and proteomes¶
The command:
sourmash sketch translate genome.fna
will output a protein sketch in ./genome.fna.sig
, calculated by translating the genome sequence in all six frames and then using the default protein sketch parameters. K-mers may include stop codons and stop codons are considered valid protein-coding sequence.
And
sourmash sketch protein -p k=25,scaled=500 -p k=27,scaled=250 genome.faa
outputs two protein sketches to ./genome.faa.sig
, one calculated with k=25 and scaled=500, the other calculated with k=27 and scaled=250.
If you want to use different encodings, you can specify them in a few ways; here is a parameter string that specifies a dayhoff encoding for the k-mers:
sourmash sketch protein -p k=25,scaled=500,dayhoff genome.faa
Translated DNA sketches for metagenomes¶
The command
sourmash sketch translate metagenome.fq
will take each read in the FASTQ file and translate the read into amino acid sequence in all six possible coding frames. No attempt is made to determine the right frame (but we are working on ways to determine this; see orpheum).
We suggest using this primarily on unassembled metagenome data. For
most microbial genomes, it is both higher quality and more efficient
to first predict the coding sequences (using e.g. prodigal) and then
use sketch protein
to build signatures.
Bulk sketch construction from many files¶
(This was added as of sourmash v4.4.0.)
The sourmash sketch fromfile
command is intended for use when
building many signatures as part of a larger workflow. It supports a
variety of options to build new signatures, parallelize
signature construction, and otherwise aid in tracking and managing
database construction.
The command
sourmash sketch fromfile datasets.csv -p dna -p protein -o database.zip
will ingest a CSV spreadsheet containing (at a minimum) the three columns
name
, genome_filename
, and protein_filename
, and build all of
the signatures requested by the parameter strings. Other columns in
this file will be ignored.
If no protein, hp, or dayhoff sketches are requested, protein_filename
can be empty for a given row; likewise, if no DNA sketches are requested,
genome_filename
can be empty for a given row.
Some of the key command-line options supported by fromfile
are:
-o/--output-signatures
will save generated signatures to any of the standard supported output formats.-o/--output-csv-info
will save a CSV file of input filenames and parameter strings for use with thesourmash sketch
command line; this can be used to construct signatures in parallel.--already-done
will take a list of existing signatures/databases to check against; signatures with matching names and parameter strings will not be rebuilt.--output-manifest-matching
will output a manifest of already-existing signatures, which can then be used withsourmash sig cat
to collate signatures across databases; see using manifests. (This providessourmash sig check
functionality insketch fromfile
.)
If you would like help and advice on constructing large databases, or
pointers to code for generating the fromfile
CSV format, please ask
on the sourmash issue tracker or gitter support channel.
More detailed documentation¶
Input formats¶
sourmash sketch
auto-detects and reads FASTQ or FASTA files, either uncompressed or compressed with gzip or bzip2. The filename doesn’t matter; sourmash sketch
will figure out the format from the file contents.
You can also stream any of these formats into sourmash sketch
via stdin by using -
as the input filename. For example,
gunzip -c data/GCF*.fna.gz | sourmash sketch dna - -o out.sig
will make a single DNA signature from all of the FASTA sequences in
data/GCF*.fna.gz
.
Note, for signatures calculated from stdin, the signature filename attribute
will be left empty, and sourmash sig describe
will output ** no name **
.
Input contents and output signatures¶
By default, sourmash sketch
will produce signatures for each input
file. If the file contains multiple FASTA/FASTQ records, these
records will be merged into the output signature. You can provide a
list of FASTA files in a text file to sourmash sketch
by passing
the text file path in via --from-file
.
If you specify --singleton
, sourmash sketch
will produce signatures for each record.
If you specify --merge <name>
, sourmash sketch will produce signatures for all input files and combine them into one signature.
The output signature(s) will be saved in locations that depend on your input parameters. By default, sourmash sketch
will put the signatures in the current directory, in a file named for the input file with a .sig
suffix. If you specify -o
, all of the signatures will be placed in that file.
Protein encodings¶
sourmash sketch protein
and sourmash sketch translate
output protein sketches by default, but can also use the dayhoff
and hp
encodings. The Dayhoff encoding collapses multiple amino acids into a smaller alphabet so that amino acids that share biochemical properties map to the same character. The hp encoding divides amino acids into hydrophobic and polar (hydrophilic) amino acids, collapsing amino acids with hydrophobic side chains together and doing the same for polar amino acids.
We are still in the process of benchmarking these encodings; ask on the issue tracker if you are interested in updates.
Note that stop characters (*
) are considered valid in all three
encodings, and are not truncated. For example, amino acid sequences
that contain stop characters at the end will produce a k-mer containing
the stop character, and that k-mer will be hashed and potentially included
in the sketch.
Parameter strings¶
The -p
argument to sourmash sketch
provides parameter strings to sourmash, and these control what signatures and sketches are calculated and output. Zero or more parameter strings can be given to sourmash. Each parameter string produces at least one sketch.
A parameter string is a space-delimited collection that can contain one or more fields, comma-separated.
k=<ksize>
- create a sketch at this k-mer size; can provide more than one time in a parameter string. Typicallyksize
is between 4 and 100.scaled=<int>
- create a scaled MinHash with k-mers sampled deterministically at 1 per<scaled>
value. This controls sketch compression rates and resolution; for example, a 5 Mbp genome sketched with a scaled of 1000 would yield approximately 5,000 k-mers.scaled
is incompatible withnum
. See our guide to signature resolution for more information.num=<int>
- create a standard MinHash with no more than<num>
k-mers kept. This will produce sketches identical to mash sketches.num
is incompatible withscaled
. See our guide to signature resolution for more information.abund
/noabund
- create abundance-weighted (or not) sketches. See Classify signatures: Abundance Weighting for details of how this works.dna
,protein
,dayhoff
,hp
- create this kind of sketch. Note thatsourmash sketch dna -p protein
andsourmash sketch protein -p dna
are invalid; please usesourmash sketch translate
for the former.
For all field names but k
, if multiple fields in a parameter string are provided, the last one encountered overrides the previous values. For k
, if multiple ksizes are specified in a single parameter string, sketches for all ksizes specified are created.
If a field isn’t specified, then the default value for that sketch type is used; so, for example, sourmash sketch dna -p abund
would calculate a sketch with k=31,scaled=1000,abund
. See below for the defaults.
Default parameters¶
The default parameters for sketches are as follows:
dna:
k=31,scaled=1000,noabund
protein:
k=10,scaled=200,noabund
dayhoff:
k=16,scaled=200,noabund
hp:
k=42,scaled=200,noabund
These were chosen by a committee of PhDs as being good defaults for an initial analysis, so, beware :).
More seriously, the DNA parameters were chosen based on the analyses done by Koslicki and Falush in MetaPalette: a k-mer Painting Approach for Metagenomic Taxonomic Profiling and Quantification of Novel Strain Variation.
The protein, dayhoff, and hp parameters were selected based on unpublished research results and/or magic formulas. We are working on publishing the results! Please ask on the issue tracker if you are curious.
More complex parameter string examples¶
Below are some more complicated sourmash sketch
command lines:
sourmash sketch dna -p k=51
- default to a scaled=1000 and noabund for a k-mer size of 51 (based on moltype/command)sourmash sketch dna -p k=31,k=51,k=21
- create one signature with multiple ksizes, using the defaults otherwisesourmash sketch translate -p k=20,num=500,protein -p k=19,num=400,dayhoff,abund -p k=30,scaled=200,hp
- create three signatures with different ksizes, moltypes, and scaled/num.
Signature naming¶
Signature names are displayed in the output for search, gather, and compare, and can be specified in a few different ways.
With default arguments, sourmash sketch
does not set a name, and the
filename is used in display output.
You can set a name using --name
, but this has the side effect of
merging the sequence records before signature creation. So, for example,
sourmash sketch dna genome1.fa genome2.fa --name genome1 -o genome.sig
would produce one signature after combining genome1.fa
and genome2.fa
.
The option --name-from-first
will set the signature name from the
first record header encountered in each file. When used with --singleton
,
this will name each signature based on the record that it is created from.
You can examine the signature name using sourmash sig describe
.
Individual signature renaming can be done from the command line using
sourmash sig split
to create individual files for each signature,
and then sourmash sig rename
.
Locations for output files¶
Signature files can contain multiple signatures and sketches. Use
sourmash sig fileinfo
to summarize the contents of a signature file,
and sourmash sig describe
to get details on the contents of a file.
You can use -o <filename>
to specify a file output location for all the output signatures; -o -
means stdout. This does not merge signatures unless --merge
is provided.
Specify --outdir
to put all the signatures in a specific directory.
Output file formats¶
Sourmash can read and write signatures in many different formats, and
sourmash sketch ... -o <filename>
supports all of the standard
output formats. Our recommendation is to output to zip files -
e.g. filename.zip
- as this is the smallest and most flexible
signature storage format.
Please see Choosing signature output formats for more details.
Downsampling and flattening signatures¶
Creating signatures is probably the most time consuming part of using sourmash, and it is the only part that requires access to the raw data. Moreover, the output signatures are generally much smaller than the input data. So, we generally suggest creating a large set of signatures once.
To support this, sourmash can do two kinds of signature conversion without going back to the raw data.
First, you can downsample num
and scaled
signatures using sourmash sig downsample
. For any sketch created with num
parameter, you can decrease that num
. And, for any scaled
parameter, you can increase the scaled
. This will decrease the size of the sketch accordingly; for example, going from a num
of 5000 to a num
of 1000 will decrease the sketch size by a factor of 5, and going from a scaled
of 1000 to a scaled
of 10000 will decrease the sketch size by a factor of 10.
(Note that decreasing num
or increasing scaled
will increase calculation speed and lower the accuracy of your results.)
Second, you can flatten abundances using sourmash sig flatten
. For any sketch created with abund
, you can convert it to a noabund
sketch. This will decrease the sketch size, although not necessarily by a lot.
Unfortunately, changing the k-mer size or using different DNA/protein encodings cannot be done on a sketch, and you need to create new signatures from the raw data for that.
Examining the output of sourmash sketch
¶
You can use sourmash sig describe
to get detailed information about the contents of a signature file, and sourmash sig fileinfo
to get a human-readable summary of the contents. This can help if you want to see exactly what a particular sourmash sketch
command does!
Filing issues and asking for help¶
We try to provide good documentation and error messages, but may not succeed in answer all your questions! So we’re happy to help out!
Please post questions on the sourmash issue tracker. If you find something confusing or buggy about the documentation or about sourmash, we’d love to fix it – for you and for everyone else!