collapse is Truvari's approach to SV merging. After leveraging bcftools to merge VCFs, truvari collapse can then iterate over the calls and create clusters of SVs that match over the provided thresholds. This is also useful when removing potentially redundant calls within a single sample.

Since collapse uses the same variant comparison engine as bench, there is a lot of overlap in the behavior. Be sure to also be familiar with the bench documentation.

Example

To start, we merge multiple VCFs (each with their own sample) and ensure there are no multi-allelic entries via:

bcftools merge -m none one.vcf.gz two.vcf.gz | bgzip > merge.vcf.gz

This will paste SAMPLE information between vcfs when calls have the exact same chrom, pos, ref, and alt. For example, consider two vcfs:

>> one.vcf:
chr1 1 ... GT 0/1
chr1 5 ... GT 1/1
>> two.vcf:
chr1 1 ... GT 1/1
chr1 7 ... GT 0/1

bcftools merge creates:

>> merge.vcf:
chr1 1 ... GT 0/1 1/1
chr1 5 ... GT 1/1 ./.
chr1 7 ... GT ./. 0/1    

This VCF can then be collapsed to allow 'fuzzier' matching than the exact merge just performed.

truvari collapse -i merge.vcf.gz -o truvari_merge.vcf -c truvari_collapsed.vcf

For example, if we collapsed our example merge.vcf by matching any calls within 3bp, we'd create:

>> truvari_merge.vcf
chr1 1 ... GT 0/1 1/1
chr1 5 ... GT 1/1 0/1
>> truvari_collapsed.vcf
chr1 7 ... GT ./. 0/1    

--choose behavior

When collapsing, the default --choose behavior is to take the first variant by position from a cluster to be written to the output while the others will be placed in the collapsed output. Other choosing options are maxqual (the call with the highest quality score) or common (the call with the highest minor allele count).

Samples with no genotype information in the kept variant will be filled by the first collapsed variant containing genotype information.

--gt

For some results, one may not want to collapse variants with conflicting genotypes from a single sample. With the --gt all parameter, variants which are present (non 0/0 or ./.) in the same sample are not collapsed. With the -gt het parameter, only variants which are both heterozygous in a sample (e.g. 0/1 and 0/1) are prevented from collapsing. The --gt het is useful for some SV callers which will redundantly call variants and typically genotype them all as 1/1.

--intra

When a single sample is run through multiple SV callers, one may wish to consolidate those results. After the bcftools merge of the VCFs, there will be one SAMPLE column per-input. With --intra, collapse will consolidate the sample information so that only a single sample column is present in the output. Since the multiple callers may have different genotypes or other FORMAT fields with conflicting information, --intra takes the first column from the VCF, then second, etc. For example, if we have an entry with:

FORMAT    RESULT1     RESULT2
GT:GQ:AD  ./.:.:3,0  1/1:20:0,30

The --intra output would be:

FORMAT    RESULT1
GT:GQ:AD  1/1:20:3,0

As you can see in this example, 1) The first sample name is the only one preserved. 2) conflicting FORMAT fields can be consolidated in a non-useful way (here the AD of 3,0 isn't informative to a 1/1 genotype). We're working to provide an API to help users write custom intra-sample consolidation scripts.

--hap mode

When using --hap, we assume phased variants from a single individual. Only the single best matching call from the other haplotype will be collapsed, and the consolidated genotype will become 1/1

For example, if we collapse anything at the same position:

chr1 1 .. GT 0|1
chr1 1 .. GT 1|0
chr1 2 .. GT 1|0

will become:

chr1 1 .. GT 1/1
chr1 2 .. GT 1|0

--chain mode

Normally, every variant in a set of variants that are collapsed together matches every other variant in the set. However, when using --chain mode, we allow 'transitive matching'. This means that all variants match to only at least one other variant in the set. In situations where a 'middle' variant has two matches that don't match each other, without --chain the locus will produce two variants whereas using --chain will produce one. For example, if we have

chr1 5 ..
chr1 7 ..
chr1 9 ..

When we collapse anything within 2bp of each other, without --chain, we output:

chr1 5 ..
chr1 9 ..

With --chain, we would collapse chr1 9 as well, producing

chr1 5 ..

Annotations

collapse produces two files. The output file has kept variants along with unanalyzed (< sizemin) variants. The collapsed file contains the variants that were collapsed into the kept variants.

The output file has only two annotations added to the INFO.

• CollapseId - Identifier of the variant when comparing to the collapse outputs.
• NumCollapsed - Number of variants collapsed into this variant
• NumConsolidated - Number of samples' genotypes consolidated into this call's genotypes

The collapsed file has all of the annotations added by bench. Note that MatchId is tied to the output file's CollapseId. See MatchIds for details.

usage: collapse [-h] -i INPUT [-o OUTPUT] [-c COLLAPSED_OUTPUT] [-f REFERENCE] [-k {first,maxqual,common}] [--debug]
                [-r REFDIST] [-p PCTSIM] [-B MINHAPLEN] [-P PCTSIZE] [-O PCTOVL] [-t] [--use-lev] [--hap] [--chain]
                [--no-consolidate] [--null-consolidate NULL_CONSOLIDATE] [-s SIZEMIN] [-S SIZEMAX] [--passonly]

Structural variant collapser

Will collapse all variants within sizemin/max that match over thresholds

options:
  -h, --help            show this help message and exit
  -i INPUT, --input INPUT
                        Comparison set of calls
  -o OUTPUT, --output OUTPUT
                        Output vcf (stdout)
  -c COLLAPSED_OUTPUT, --collapsed-output COLLAPSED_OUTPUT
                        Where collapsed variants are written (collapsed.vcf)
  -f REFERENCE, --reference REFERENCE
                        Indexed fasta used to call variants
  -k {first,maxqual,common}, --keep {first,maxqual,common}
                        When collapsing calls, which one to keep (first)
  --debug               Verbose logging
  --hap                 Collapsing a single individual's haplotype resolved calls (False)
  --chain               Chain comparisons to extend possible collapsing (False)
  --no-consolidate      Skip consolidation of sample genotype fields (True)
  --null-consolidate NULL_CONSOLIDATE
                        Comma separated list of FORMAT fields to consolidate into the kept entry by taking the first non-null
                        from all neighbors (None)

Comparison Threshold Arguments:
  -r REFDIST, --refdist REFDIST
                        Max reference location distance (500)
  -p PCTSIM, --pctsim PCTSIM
                        Min percent allele sequence similarity. Set to 0 to ignore. (0.95)
  -B MINHAPLEN, --minhaplen MINHAPLEN
                        Minimum haplotype sequence length to create (50)
  -P PCTSIZE, --pctsize PCTSIZE
                        Min pct allele size similarity (minvarsize/maxvarsize) (0.95)
  -O PCTOVL, --pctovl PCTOVL
                        Min pct reciprocal overlap (0.0) for DEL events
  -t, --typeignore      Variant types don't need to match to compare (False)
  --use-lev             Use the Levenshtein distance ratio instead of edlib editDistance ratio (False)

Filtering Arguments:
  -s SIZEMIN, --sizemin SIZEMIN
                        Minimum variant size to consider for comparison (50)
  -S SIZEMAX, --sizemax SIZEMAX
                        Maximum variant size to consider for comparison (50000)
  --passonly            Only consider calls with FILTER == PASS