Add support for matching VCF lines by ID

bcf_sr_sort.c

@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2017-2021 Genome Research Ltd.
+    Copyright (C) 2017-2024 Genome Research Ltd.
 
     Author: Petr Danecek <[email protected]>
 
@@ -32,6 +32,7 @@
 #include "htslib/khash_str2int.h"
 #include "htslib/kbitset.h"
 
+// Variant types and pair-wise compatibility of their combinations, see bcf_sr_init_scores()
 #define SR_REF   1
 #define SR_SNP   2
 #define SR_INDEL 4
@@ -366,7 +367,7 @@ static int bcf_sr_sort_set(bcf_srs_t *readers, sr_sort_t *srt, const char *chr,
     // group VCFs into groups, each with a unique combination of variants in the duplicate lines
     int ireader,ivar,irec,igrp,ivset,iact;
     for (ireader=0; ireader<readers->nreaders; ireader++) srt->vcf_buf[ireader].nrec = 0;
-    for (iact=0; iact<srt->nactive; iact++)
+    for (iact=0; iact<srt->nactive; iact++) // process each of the active readers, ie which still have a record to process
     {
         ireader = srt->active[iact];
         bcf_sr_t *reader = &readers->readers[ireader];
@@ -384,6 +385,11 @@ static int bcf_sr_sort_set(bcf_srs_t *readers, sr_sort_t *srt, const char *chr,
             srt->off[srt->noff++] = srt->str.l;
             size_t beg  = srt->str.l;
             int end_pos = -1;
+            if ( srt->pair & BCF_SR_PAIR_ID )
+            {
+                kputs(line->d.id,&srt->str);
+                kputc(':',&srt->str);
+            }
             for (ivar=1; ivar<line->n_allele; ivar++)
             {
                 if ( ivar>1 ) kputc(',',&srt->str);
@@ -417,7 +423,10 @@ static int bcf_sr_sort_set(bcf_srs_t *readers, sr_sort_t *srt, const char *chr,
             }
 
             // Create new variant or attach to existing one. But careful, there can be duplicate
-            // records with the same POS,REF,ALT (e.g. in dbSNP-b142)
+            // records with the same POS,REF,ALT (e.g. in dbSNP-b142). In such case, use a
+            // hash table (srt->var_str2int) and a counter (var_idx) to ensure they are
+            // treated as separate variants, while still allowing them to be matched
+            // between readers.
             char *var_str = beg + srt->str.s;
             int ret, var_idx = 0, var_end = srt->str.l;
             while ( 1 )
@@ -435,6 +444,7 @@ static int bcf_sr_sort_set(bcf_srs_t *readers, sr_sort_t *srt, const char *chr,
             }
             if ( ret==-1 )
             {
+                // the variant is not present, insert
                 ivar = srt->nvar++;
                 hts_expand0(var_t,srt->nvar,srt->mvar,srt->var);
                 srt->var[ivar].nvcf = 0;

bcf_sr_sort.h

@@ -55,6 +55,9 @@ typedef struct
 }
 var_t;
 
+// Group is a set of variants in duplicate records within one VCF. They are identified with a key (used only
+// for debugging), such as C>A,C>G;C>T. Commas separate alleles in a multiallelic record, semicolons separate
+// VCF lines.
 typedef struct
 {
     char *key;              // only for debugging
@@ -67,7 +70,7 @@ typedef struct
 {
     int nvar, mvar, *var;   // list of compatible variants that can be output together
     int cnt;                // number of readers in this group
-    kbitset_t *mask;        // which groups are populated in this set (replace with expandable bitmask)
+    kbitset_t *mask;        // which groups are populated in this set
 }
 varset_t;
 
@@ -100,8 +103,13 @@ sr_sort_t;
 sr_sort_t *bcf_sr_sort_init(sr_sort_t *srt);
 void bcf_sr_sort_reset(sr_sort_t *srt);
 int bcf_sr_sort_next(bcf_srs_t *readers, sr_sort_t *srt, const char *chr, hts_pos_t pos);
+
+// initialize a new position using the i-th reader
 int bcf_sr_sort_set_active(sr_sort_t *srt, int i);
+
+// add i-th reader with the same position, assumed bcf_sr_sort_set_active() was called with another reader
 int bcf_sr_sort_add_active(sr_sort_t *srt, int i);
+
 void bcf_sr_sort_destroy(sr_sort_t *srt);
 void bcf_sr_sort_remove_reader(bcf_srs_t *readers, sr_sort_t *srt, int i);
 

htslib/synced_bcf_reader.h

@@ -1,7 +1,7 @@
 /// @file htslib/synced_bcf_reader.h
 /// Stream through multiple VCF files.
 /*
-    Copyright (C) 2012-2017, 2019-2023 Genome Research Ltd.
+    Copyright (C) 2012-2017, 2019-2024 Genome Research Ltd.
 
     Author: Petr Danecek <[email protected]>
 
@@ -89,6 +89,7 @@ extern "C" {
 #define BCF_SR_PAIR_SNP_REF    (1<<4)  // allow REF-only records with SNPs
 #define BCF_SR_PAIR_INDEL_REF  (1<<5)  // allow REF-only records with indels
 #define BCF_SR_PAIR_EXACT      (1<<6)  // require the exact same set of alleles in all files
+#define BCF_SR_PAIR_ID         (1<<7)  // require matching IDs (overlap)
 #define BCF_SR_PAIR_BOTH       (BCF_SR_PAIR_SNPS|BCF_SR_PAIR_INDELS)
 #define BCF_SR_PAIR_BOTH_REF   (BCF_SR_PAIR_SNPS|BCF_SR_PAIR_INDELS|BCF_SR_PAIR_SNP_REF|BCF_SR_PAIR_INDEL_REF)