Liftover drop-tags finds no matching tags

[meyerkm]

Run command:
bcftools +liftover -Oz -o testvcf_output.vcf.gz testvcf_input.vcf.gz -- -s source_fasta.fa -f reference.fa -c chainfile.chain.gz --reject testvcf.rejected.vcf.gz

Error #1:

INFO/AF is handled by AF rule
Number of elements in the VCF record AF should be 1 but 2 found
Use --drop-tags INFO/AF to skip this error

Which arrises in the case of needing to swap alleles. All files do have two values for the INFO/AF field , i.e. AF=0.5,0.3
Attempted fix:
bcftools +liftover -Oz -o testvcf_output.vcf.gz testvcf_input.vcf.gz -- -s source_fasta.fa -f reference.fa -c chainfile.chain.gz --reject testvcf.rejected.vcf.gz --drop-tags [INFO/AF]

Error#2:
No matching tag [INFO/AF]

As a check, generally querying that tag in the VCF does work :
bcftools query -f '%INFO/AF' testvcf_input.vcf.gz

Maybe there is some trick to identifying the drop-tags? I have tried various inputs/string combinations for the drop-tags option without any luck.

[freeseek]

The correct syntax should be --drop-tags INFO/AF. But it is a bit worrisome that you have two 2 INFO/AF elements where 1 is expected. The INFO/AF field should be a Number=A field, that is, a field with one number for each alternate allele. This is mandated by the VCF specification. How do you interpret and INFO/AF field as AF=0.5,0.3 for a variant with one alternate allele?

[meyerkm]

Thanks for the indication, unfortunately with that syntax I still get the error from above, as if it doesn't recognize that the flag was even set.

Run command :
bcftools +liftover -Oz -o testvcf_output.vcf.gz testvcf_input.vcf.gz -- -s source_fasta.fa -f reference.fa -c chainfile.chain.gz --reject testvcf.rejected.vcf.gz --drop-tags INFO/AF

Error :

INFO/AF is handled by AF rule
WARNING: bcftools version mismatch .. bcftools at 1.18, the plugin "liftover" at 1.19
Number of elements in the VCF record AF should be 1 but 2 found
Use --drop-tags INFO/AF to skip this error

[freeseek]

Try again using the development version from here and see if fixes the issue

[jjfarrell]

If the site is multi-allelic (2 alternate alleles), wouldn't there be a corresponding two AF values. Does running bcftools norm -m -any eliminate the error when running liftover?

…

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[freeseek]

Yes, if the site has two alternate alleles then INFO/AF should have two values but the problem for @meyerkm is likely a site with one alternate allele and two values from the provided explanation. A site with two alternate alleles and two INFO/AF values will work just as intended with BCFtools/liftover while BCFtools/norm will also throw an error when trying to split a multi-allelic site where the Number=A INFO field has an incorrect number of values

[meyerkm]

Correct @freeseek , yes I have one alternate allele but two values in the INFO/AF field. I have an AF value from two samples. I was hoping this --drop-tags flag would be able to allow things to carry-on irrespective of this detail. I am going to remove the secondary AF value that isn't the control, thus I won't have to utilize the --drop-tags.

But I can of course test the develop version you posted above, as having the drop-tags functionality work in a catch-all way may otherwise be useful!

[meyerkm]

The develop version you have listed above does work for those SWAP cases with the --drop-tags!

Same run command, as above, but with the development version of liftover:
bcftools +liftover -Oz -o testvcf_output.vcf.gz testvcf_input.vcf.gz -- -s source_fasta.fa -f reference.fa -c chainfile.chain.gz --reject testvcf.rejected.vcf.gz --drop-tags INFO/AF

Output:

INFO/AF is handled by DROP rule
WARNING: bcftools version mismatch .. bcftools at 1.18, the plugin "liftover" at 1.19
Lines   total/swapped/reference added/rejected:	493/3/0/0