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1D/2D indexing and querying on bgzipped text file with a pair of genomic coordinates

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pairix

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  • Pairix is a tool for indexing and querying on a block-compressed text file containing pairs of genomic coordinates.

  • Pairix is a stand-alone C program that was written on top of tabix (https://github.com/samtools/tabix) as a tool for the 4DN-standard pairs file format describing Hi-C data: pairs_format_specification.md

  • However, Pairix can be used as a generic tool for indexing and querying any bgzipped text file containing genomic coordinates, for either 2D- or 1D- indexing and querying.

  • For example: given the custom text file below, you want to extract specific lines from the Pairs file further below. An awk command would read the Pairs file from beginning to end. Pairix creates an index and uses it to access the file from a relevant position by taking advantage of bgzf compression, allowing for a fast query on large files.

    Some custom text file

    chr1  10000  20000 chr2  30000  50000  3.5
chr1  30000  40000 chr3  10000  70000  4.6

    Pairs format

    ## pairs format v1.0
#sorted: chr1-chr2-pos1-pos2
#shape: upper triangle
#chromsize: chr1 249250621
#chromsize: chr2 243199373
#chromsize: chr3 198022430
...
#genome_assembly: hg38
#columns: readID chr1 pos1 chr2 pos2 strand1 strand2
EAS139:136:FC706VJ:2:2104:23462:197393 chr1 10000 chr1 20000 + +
EAS139:136:FC706VJ:2:8762:23765:128766 chr1 50000 chr1 70000 + +
EAS139:136:FC706VJ:2:2342:15343:9863 chr1 60000 chr2 10000 + +
EAS139:136:FC706VJ:2:1286:25:275154 chr1 30000 chr3 40000 + -

  • Bgzip can be found either in this repo or https://github.com/samtools/tabix (original).

Table of contents


Availability

  • Pairix is available as a stand-alone command-line program, a python library (pypairix), and an R package (Rpairix https://github.com/4dn-dcic/Rpairix)
  • Various utils including bam2pairs, merged_nodups2pairs.pl, pairs_merger etc. are available within this repo.
  • The bgzip program that is provided as part of the repo is identical to the original program in https://github.com/samtools/tabix.

Input file format

  • For 2D indexing, the input file of paired coordinates must first be sorted by the two chromosome columns and then by the first genomic position column. For 1D indexing, the file must be sorted by a chromosome column and then by a position column.
  • The input file must be compressed using bgzip and is either tab-delimited or space-delimited.
  • The resulting index file will be given the extension .px2.

Pairix

Installation for pairix

git clone https://github.com/4dn-dcic/pairix
cd pairix
make
# Add the bin path to PATH for pairix, bgzip, pairs_merger and stream_1d
# In order to use utils, add util path to PATH
# In order to use bam2pairs, add util/bam2pairs to PATH
# eg: PATH=~/git/pairix/bin/:~/git/pairix/util:~/git/pairix/util/bam2pairs:$PATH

Alternatively, conda install pairix can be used to install both Pairix and Pypairix together. This requires Anaconda or Miniconda.

If you get an error message saying zlib cannot be found, try installing zlib first as below before make.

# ubuntu
sudo apt-get install zlib1g-dev

# centos
sudo yum install zlib-devel


Usage for pairix

Compression

bgzip textfile

Indexing

pairix textfile.gz  # for recognized file extension
pairix -p <preset> textfile.gz
pairix -s<chr1_column> [-d<chr2_column>] -b<pos1_start_column> -e<pos1_end_column> [-u<pos2_start_column> -v<pos2_end_column>] [-T] textfile.gz    # u, v is required for full 2d query.
  • column indices are 1-based.
  • use -T option for a space-delimited file.
  • use -f option to overwrite an existing index file.
  • presets can be used for indexing : pairs, merged_nodups, old_merged_nodups for 2D indexing, gff, vcf, bed, sam for 1D indexing. Default is pairs.
  • For the recognized file extensions, the -p option can be dropped: .pairs.gz, .vcf.gz, gff.gz, bed.gz, sam.gz
  • Custom column specification (-s, -d, -b, -e, -u, -v) overrides file extension recognition. The custom specification must always have at least chr1_column (-s).
  • use -w <character> option to change region split character (default '|', see below the Querying section for details). This is useful when your chromosome names contain the '|' character. (e.g. -w '^')

Querying

pairix textfile.gz region1 [region2 [...]]  ## region is in the following format.

# for 1D indexed file
pairix textfile.gz '<chr>:<start>-<end>' '<chr>:<start>-<end>' ...

# for 2D indexed file
pairix [-a] textfile.gz '<chr1>:<start1>-<end1>|<chr2>:<start2>-<end2>' ...    # make sure to quote so '|' is not interpreted as a pipe.
pairix [-a] textfile.gz '*|<chr2>:<start2>-<end2>'  # wild card is accepted for 1D query on 2D indexed file
pairix [-a] textfile.gz '<chr1>:<start1>-<end1>|*' # wild card is accepted for 1D query on 2D indexed file
  • The -a option (auto-flip) flips query when a given chromosome pair doesn't exist.
pairix -a samples/test_4dn.pairs.gz 'chrY|chrX' |head
SRR1658581.13808070	chrX	359030	chrY	308759	-	+
SRR1658581.1237993	chrX	711481	chrY	3338402	+	-
SRR1658581.38694206	chrX	849049	chrY	2511913	-	-
SRR1658581.6691868	chrX	1017548	chrY	967955	+	-
SRR1658581.2398986	chrX	1215519	chrY	569356	-	+
SRR1658581.21090183	chrX	1406586	chrY	2621557	+	-
SRR1658581.35447261	chrX	1501769	chrY	1458068	+	-
SRR1658581.26384827	chrX	1857703	chrY	1807309	-	+
SRR1658581.13824346	chrX	2129016	chrY	2411576	-	-
SRR1658581.6160690	chrX	2194708	chrY	2485859	-	-

using a file listing query regions

pairix -L textfile.gz regionfile1 [regionfile2 [...]] # region file contains one region string per line
  • The default region split character is '|', which can be changed by using the -w option when building an index.

List of chromosome pairs

This command prints out all chromosome pairs in the file.

pairix -l textfile.gz

Total linecount

This is equivalent to but much faster than gunzip -c | wc -l.

pairix -n textfile.gz

Print out region split character

By default '|' is used to split the two genomic regions, but in some cases, a different character is used and it is stored in the index. This command prints out the character used for a specific pairs file.

pairix -W textfile.gz

Print out number of bgzf blocks that span each chromosome pair.

This command prints out the number of bgzk blocks for all chromosome pairs.

pairix -B textfile.gz

Usage examples for pairix

Preparing a 4dn-style pairs file. This is a double-chromosome-block sorted test file.

(column 2 and 4 are chromosomes (chr1 and chr2), column 3 is position of the first coordinate (pos1)).

# sorting & bgzipping
sort -k2,2 -k4,4 -k3,3n -k5,5n samples/4dn.bsorted.chr21_22_only.pairs |bgzip -c > samples/4dn.bsorted.chr21_22_only.pairs.gz

# indexing
pairix -f samples/4dn.bsorted.chr21_22_only.pairs.gz
# The above command is equivalent to: pairix -f -s2 -b3 -e3 -d4 -u5 samples/4dn.bsorted.chr21_22_only.pairs.gz
# The above command is also equivalent to: pairix -f -p pairs samples/4dn.bsorted.chr21_22_only.pairs.gz
# Pairs extension .pairs.gz is automatically recognized.

Preparing a double-chromosome-block sorted merged_nodups.txt file (Juicer-style pairs file)

(columns 2 and 6 are chromosomes (chr1 and chr2), and column 3 is position of the first coordinate (pos1)).

# sorting & bgzipping
sort -t' ' -k2,2 -k6,6 -k3,3n -k7,7n merged_nodups.txt |bgzip -c > samples/merged_nodups.space.chrblock_sorted.subsample3.txt

#indexing
pairix -f -p merged_nodups samples/merged_nodups.space.chrblock_sorted.subsample3.txt.gz
# The above command is equivalent to : pairix -f -s2 -d6 -b3 -e3 -u7 -T samples/merged_nodups.space.chrblock_sorted.subsample3.txt.gz

querying

semi 2D query with two chromosomes

pairix samples/test_4dn.pairs.gz 'chr21|chr22'
SRR1658581.33025893	chr21	9712946	chr22	21680462	-	+
SRR1658581.9428560	chr21	10774937	chr22	37645396	-	+
SRR1658581.8816993	chr21	11171003	chr22	33169971	+	+
SRR1658581.10673815	chr21	16085548	chr22	35451128	+	-
SRR1658581.2504661	chr21	25672432	chr22	21407301	-	-
SRR1658581.40524826	chr21	28876237	chr22	42449178	+	+
SRR1658581.8969171	chr21	33439464	chr22	43912252	-	-
SRR1658581.6842680	chr21	35467614	chr22	33478115	+	+
SRR1658581.15363628	chr21	37956917	chr22	21286436	-	-
SRR1658581.3572823	chr21	40651454	chr22	41358228	-	-
SRR1658581.50137399	chr21	42446807	chr22	49868647	-	+
SRR1658581.11358652	chr21	43768599	chr22	40759935	-	-
SRR1658581.4127782	chr21	45142744	chr22	36929446	+	+
SRR1658581.38401094	chr21	46989766	chr22	45627553	-	+
SRR1658581.34261420	chr21	48113817	chr22	51138644	+	-

semi 2D query with a chromosome and a range

pairix samples/test_4dn.pairs.gz 'chr21:10000000-20000000|chr22'
SRR1658581.9428560	chr21	10774937	chr22	37645396	-	+
SRR1658581.8816993	chr21	11171003	chr22	33169971	+	+
SRR1658581.10673815	chr21	16085548	chr22	35451128	+	-

full 2D query with two ranges

pairix samples/test_4dn.pairs.gz 'chr21:10000000-20000000|chr22:30000000-35000000'
SRR1658581.8816993	chr21	11171003	chr22	33169971	+	+

full 2D multi-query

pairix samples/test_4dn.pairs.gz 'chr21:10000000-20000000|chr22:30000000-35000000' 'chrX:100000000-110000000|chrX:150000000-170000000'
SRR1658581.8816993	chr21	11171003	chr22	33169971	+	+
SRR1658581.39700722	chrX	100748075	chrX	154920234	+	+
SRR1658581.36337371	chrX	104718152	chrX	151646254	+	-
SRR1658581.49591338	chrX	104951264	chrX	154363440	+	+
SRR1658581.46205223	chrX	105732382	chrX	155162659	+	-
SRR1658581.32048997	chrX	107326643	chrX	151899433	-	+

Wild-card 2D query

pairix samples/test_4dn.pairs.gz 'chr21:9000000-9700000|*'
SRR1658581.18102003	chr21	9582382	chr21	9733996	+	+
SRR1658581.10121427	chr21	9665774	chr4	49203518	+	-
SRR1658581.1019708	chr21	9496682	chr4_gl000193_random	48672	+	+
SRR1658581.44516250	chr21	9662891	chr6	7280832	-	+
SRR1658581.15515341	chr21	9549471	chr9	68384076	+	+
SRR1658581.51399686	chr21	9687495	chrUn_gl000221	87886	+	+
SRR1658581.25532108	chr21	9519859	chrUn_gl000226	6821	+	-
SRR1658581.22081000	chr21	9659013	chrUn_gl000232	19626	-	-
SRR1658581.34308344	chr21	9532618	chrX	61793091	-	+

pairix samples/test_4dn.pairs.gz '*|chr21:9000000-9700000'
SRR1658581.21313395	chr1	25612365	chr21	9679403	+	-
SRR1658581.46040617	chr1	143255816	chr21	9663103	+	+
SRR1658581.54790470	chr14	101961336	chr21	9481250	+	+
SRR1658581.38248307	chr18	18518988	chr21	9452846	-	+
SRR1658581.9143926	chr2	90452598	chr21	9486716	+	-

Symmetric query - 1D query on a 2D-index file is interpreted as a symmetric 2D query. The two commands below are equivalent.

pairix samples/test_4dn.pairs.gz 'chr22:50000000-60000000'
SRR1658581.11011611	chr22	50224888	chr22	50225362	+	-
SRR1658581.37423580	chr22	50528835	chr22	50529355	+	-
SRR1658581.20673732	chr22	50638372	chr22	51062837	+	-
SRR1658581.38906907	chr22	50661701	chr22	50813018	+	-
SRR1658581.7631402	chr22	50767962	chr22	50773437	-	+
SRR1658581.31517355	chr22	50910780	chr22	50911083	+	-
SRR1658581.31324262	chr22	50991542	chr22	50991895	+	-
SRR1658581.46124457	chr22	51143411	chr22	51143793	+	-
SRR1658581.23040702	chr22	51229529	chr22	51229809	+	-

pairix samples/test_4dn.pairs.gz 'chr22:50000000-60000000|chr22:50000000-60000000'
SRR1658581.11011611	chr22	50224888	chr22	50225362	+	-
SRR1658581.37423580	chr22	50528835	chr22	50529355	+	-
SRR1658581.20673732	chr22	50638372	chr22	51062837	+	-
SRR1658581.38906907	chr22	50661701	chr22	50813018	+	-
SRR1658581.7631402	chr22	50767962	chr22	50773437	-	+
SRR1658581.31517355	chr22	50910780	chr22	50911083	+	-
SRR1658581.31324262	chr22	50991542	chr22	50991895	+	-
SRR1658581.46124457	chr22	51143411	chr22	51143793	+	-
SRR1658581.23040702	chr22	51229529	chr22	51229809	+	-

Query using a region file

cat samples/test.regions
chr1:1-50000|*
*|chr1:1-50000
chr2:1-20000|*
*|chr2:1-20000

cat samples/test.regions2
chrX:100000000-110000000|chrY
chr19:1-300000|chr19

bin/pairix -L samples/test_4dn.pairs.gz samples/test.regions samples/test.regions2
SRR1658581.49364897	chr1	36379	chr20	62713042	+	+
SRR1658581.31672330	chr1	12627	chr9	23963238	+	-
SRR1658581.22713561	chr1	14377	chrX	107423076	-	+
SRR1658581.31992022	chrX	108223782	chrY	5017118	-	-
SRR1658581.55524746	chr19	105058	chr19	105558	+	-

1D indexing on a regular vcf file, bgzipped.

1D indexing

pairix -f samples/SRR1171591.variants.snp.vqsr.p.vcf.gz
# The above command is equivalent to : pairix -f -s1 -b2 -e2 samples/SRR1171591.variants.snp.vqsr.p.vcf.gz
# The above command is also equivalent to : pairix -f -p vcf samples/SRR1171591.variants.snp.vqsr.p.vcf.gz
# The extension `.vcf.gz` is automatically recognized.

1D query

pairix samples/SRR1171591.variants.snp.vqsr.p.vcf.gz chr10:1-4000000
chr10	3463966	.	C	T	51.74	PASS	AC=2;AF=1.00;AN=2;DB;DP=2;Dels=0.00;FS=0.000;HaplotypeScore=0.0000;MLEAC=2;MLEAF=1.00;MQ=50.00;MQ0=0;POSITIVE_TRAIN_SITE;QD=25.87;VQSLOD=7.88;culprit=FS	GT:AD:DP:GQ:PL	1/1:0,2:2:6:79,6,0
chr10	3978708	rs29320259	T	C	1916.77	PASS	AC=2;AF=1.00;AN=2;BaseQRankSum=1.016;DB;DP=67;Dels=0.00;FS=0.000;HaplotypeScore=629.1968;MLEAC=2;MLEAF=1.00;MQ=50.00;MQ0=0;MQRankSum=0.773;POSITIVE_TRAIN_SITE;QD=28.61;ReadPosRankSum=0.500;VQSLOD=3.29;culprit=FS	GT:AD:DP:GQ:PL	1/1:3,64:67:70:1945,70,0
chr10	3978709	.	G	A	1901.77	PASS	AC=2;AF=1.00;AN=2;BaseQRankSum=0.677;DB;DP=66;Dels=0.00;FS=0.000;HaplotypeScore=579.9049;MLEAC=2;MLEAF=1.00;MQ=50.00;MQ0=0;MQRankSum=0.308;POSITIVE_TRAIN_SITE;QD=28.81;ReadPosRankSum=0.585;VQSLOD=3.24;culprit=FS	GT:AD:DP:GQ:PL	1/1:3,63:66:73:1930,73,0

Pypairix

Installation for pypairix

# to install the python module pypairix,
pip install pypairix
# you may need to install python-dev for some ubuntu releases.

# or
cd pairix
python setup.py install

# testing the python module
python test/test.py

Alternatively, conda install pairix can be used to install both Pairix and Pypairix together. This requires Anaconda or Miniconda.


Usage examples for pypairix

# to import and use python module pypairix, add the following in your python script.
import pypairix

# 2D query usage example 1 with `query2D(chrom, start, end, chrom2, start2, end2)`
tb=pypairix.open("textfile.gz")
it = tb.query2D(chrom, start, end, chrom2, start2, end2)
for x in it:
   print(x)

# 2D query usage example 1 with *autoflip* with `query2D(chrom, start, end, chrom2, start2, end2, 1)`
# Autoflip: if the queried chromosome pair does not exist in the pairs file, query the flipped pair.
tb=pypairix.open("textfile.gz")
it = tb.query2D(chrom2, start2, end2, chrom1, start1, end1, 1)
for x in it:
   print(x)

# 2D query usage example 2 with `querys2D(querystr)`
tb=pypairix.open("textfile.gz")
querystr='{}:{}-{}|{}:{}-{}'.format(chrom, start, end, chrom2, start2, end2)
it = tb.querys2D(querystr)
for x in it:
   print(x)

# 2D query usage example with wild card
tb=pypairix.open("textfile.gz")
querystr='{}:{}-{}|*'.format(chrom, start, end)
it = tb.querys2D(querystr)
for x in it:
   print(x)

# 2D query usage example 3, with *autoflip* with `querys2D(querystr, 1)`
# Autoflip: if the queried chromosome pair does not exist in the pairs file, query the flipped pair.
tb=pypairix.open("textfile.gz")
querystr='{}:{}-{}|{}:{}-{}'.format(chrom2, start2, end2, chrom, start, end)
it = tb.querys2D(querystr, 1)
for x in it:
   print(x)

# 1D query on 2D indexed file
tb=pypairix.open("textfile.gz")
querystr='{}:{}-{}'.format(chrom, start, end)
it = tb.querys2D(querystr)
# The above two lines are equivalent to the following:
# querystr='{}:{}-{}|{}:{}-{}'.format(chrom, start, end, chrom, start, end)
# it = tb.querys2D(querystr)
for x in it:
   print(x)

# 1D query on 1D indexed file, example 1
tb=pypairix.open("textfile.gz")
it = tb.query(chrom, start, end)
for x in it:
   print(x)

# 1D query on 1D indexed file, example 2
tb=pypairix.open("textfile.gz")
querystr='{}:{}-{}'.format(chrom, start, end)
it = tb.querys(querystr)
for x in it:
   print(x)

# get the list of (chr-pair) blocks
tb=pypairix.open("textfile.gz")
chrplist = tb.get_blocknames()
print str(chrplist)

# get the column index (0-based)
tb=pypairix.open("textfile.gz")
print( tb.get_chr1_col() )
print( tb.get_chr2_col() )
print( tb.get_startpos1_col() )
print( tb.get_startpos2_col() )
print( tb.get_endpos1_col() )
print( tb.get_endpos2_col() )

# check if key exists (key is a chromosome pair for a 2D-indexed file, or a chromosome for a 1D-indexed file)
tb=pypairix.open("textfile.gz")
print( tb.exists("chr1|chr2") )  # 1 if exists, 0 if not.
print( tb.exists2("chr1","chr2") )  # 1 if exists, 0 if not.

# get header
tb=pypairix.open("textfile.gz")
print (tb.get_header())

# get chromsize
tb=pypairix.open("textfile.gz")
print (tb.get_chromsize())

# get the number of bgzf blocks that span a given chromosome pair
tb=pypairix.open("textfile.gz")
print (tb.bgzf_block_count("chr1", "chr2"))

# check if an indexed file is a triangle
tb=pypairix.open("textfile.gz")
print (tb.check_triangle())

Rpairix


Utils

bam2pairs

  • This script converts a bam file to a 4dn style pairs file, sorted and indexed.
  • See util/bam2pairs/README.md for more details.

process_merged_nodup.sh

  • This script sorts, bgzips and indexes a newer version of merged_nodups.txt file with strand1 as the first column.
Usage: process_merged_nodup.sh <merged_nodups.txt>

process_old_merged_nodup.sh

  • This script sorts, bgzips and indexes an old version of merged_nodups.txt file with readID as the first column.
Usage: process_old_merged_nodup.sh <merged_nodups.txt>

merged_nodup2pairs.pl

  • This script converts Juicer's merged_nodups.txt format to 4dn-style pairs format. It requires pairix and bgzip binaries in PATH.
Usage: merged_nodup2pairs.pl <input_merged_nodups.txt> <chromsize_file> <output_prefix>
  • An example output file (bgzipped and indexed) looks as below.
## pairs format v1.0
#sorted: chr1-chr2-pos1-pos2
#shape: upper triangle
#chromsize: 1 249250621
#chromsize: 2 243199373
...
#columns: readID chr1 pos1 chr2 pos2 strand1 strand2 frag1 frag2
SRR1658650.8850202.2/2	1	16944943	1	151864549	-	+	45178	333257
SRR1658650.8794979.1/1	1	21969282	1	50573348	-	-	59146	140641
SRR1658650.6209714.1/1	1	31761397	1	32681095	-	+	88139	90865
SRR1658650.6348458.2/2	1	40697468	1	40698014	+	-	113763	113763
SRR1658650.12316544.1/1	1	41607001	1	41608253	+	+	116392	116398

old_merged_nodup2pairs.pl

  • This script converts Juicer's old merged_nodups.txt format to 4dn-style pairs format. It requires pairix and bgzip binaries in PATH.
Usage: old_merged_nodup2pairs.pl <input_merged_nodups.txt> <output_prefix>
  • An example output file (bgzipped and indexed) looks as below.
## pairs format v1.0
#sorted: chr1-chr2-pos1-pos2
#shape: upper triangle
#chromsize: 1 249250621
#chromsize: 2 243199373
...
#columns: readID chr1 pos1 chr2 pos2 strand1 strand2 frag1 frag2
SRR1658650.8850202.2/2	1	16944943	1	151864549	-	+	45178	333257
SRR1658650.8794979.1/1	1	21969282	1	50573348	-	-	59146	140641
SRR1658650.6209714.1/1	1	31761397	1	32681095	-	+	88139	90865
SRR1658650.6348458.2/2	1	40697468	1	40698014	+	-	113763	113763
SRR1658650.12316544.1/1	1	41607001	1	41608253	+	+	116392	116398

fragment_4dnpairs.pl

  • This script adds juicer-style fragment information to 4DN-DCIC style pairs file.
Usage: gunzip -c <input.pairs.gz> | fragment_4dnpairs.pl [--allow-replacement] - <out.pairs> <juicer-style-restriction-site-file>

duplicate_header_remover.pl

  • This script removes duplicate headers from a pairs file (either ungzipped or streamed). This is useful when you accidentally created a wrong pairs file with duplicate headers. The order of the headers doesn't change. Duplicates don't necessarily have to be in consecutive lines.
Usage: gunzip -c <input.pairs.gz> | duplicate_header_remover.pl - | bgzip -c > <out.pairs.gz>

column_remover.pl

  • This script removes columns from a pairs file (either ungzipped or streamed).
# The following removes multiple columns from both header and content. The columns to be removed should be referred to by column names.
Usage: gunzip -c <input.pairs.gz> | column_remover.pl - <colname1> [<colname2> ...] | bgzip -c > <out.pairs.gz>

# The following removes a single column from only the content. The column to be removed should be referred to by column index (0-based).
Usage: gunzip -c <input.pairs.gz> | column_remover.pl --do-not-fix-header - <colindex> | bgzip -c > <out.pairs.gz>

Pairs_merger

Pairs_merger is a tool that merges indexed pairs files that are already sorted, creating a sorted output pairs file. Pairs_merger uses a k-way merge sort algorithm starting with k file streams. Specifically, it loops over a merged iterator composed of a dynamically sorted array of k iterators. It neither requires additional memory nor produces any temporary files.

Usage for pairs_merger

pairs_merger <in1.gz> <in2.gz> <in3.gz> ... > <out.txt>
# Each of the input files must have a .px2 index file.
bgzip out.txt

## or pipe to bgzip
pairs_merger <in1.gz> <in2.gz> <in3.gz> ... | bgzip -c > <out.gz>

# To index the output file as well
# use the appropriate options according to the output file format.
pairix [options] out.gz

Usage examples for pairs_merger

bin/pairs_merger samples/merged_nodups.space.chrblock_sorted.subsample2.txt.gz samples/merged_nodups.space.chrblock_sorted.subsample3.txt.gz | bin/bgzip -c > out.gz
bin/pairix -f -p merged_nodups out.gz
# The above command is equivalent to : bin/pairix -f -s2 -d6 -b3 -e3 -u7 -T out.gz

merge-pairs.sh

Merge-pairs.sh is a merger specifically for the 4DN pairs file. This merger is header-friendly. The input pairs files do not need to be indexed, but need to be sorted properly.

Usage for merge-pairs.sh

# The following command will create outprefix.pairs.gz and outprefix.pairs.gz.px2, given in1.pairs.gz, in2.pairs.gz, ....
merge-pairs.sh <outprefix> <in1.pairs.gz> <in2.pairs.gz> ...

Usage examples for merge-pairs.sh

util/merge-pairs.sh output sample1.pairs.gz sample2.pairs.gz

Streamer_1d

Streamer_1d is a tool that converts a 2d-sorted pairs file to a 1d-sorted stream (sorted by chr1-chr2-pos1-pos2 -> sorted by chr1-pos1). This tool uses a k-way merge sort on k file pointers on the same input file, operates linearly without producing any temporary files. Currently, the speed is actually slower than unix sort and is therefore not recommended.

Usage for streamer_1d

streamer_1d <in.2d.gz> > out.1d.pairs
streamer_1d <in.2d.gz> | bgzip -c > out.1d.pairs.gz

Usage Examples for streamer_1d

bin/streamer_1d samples/merged_nodups.space.chrblock_sorted.subsample2.txt.gz | bgzip -c > out.1d.pairs.gz

FAQ for streamer_1d

The tool creates many file pointers for the input file, which is equivalent to opening many files simultaneously. Your OS may have a limit on the number of files that can be open at a time. For example, for Mac El Captain and Sierra, it is by default set to 256. This is usually enough, but in case the number of chromosomes in your pairs file happen to be larger than or close to this limit, the tool may produce an error message saying file limit is exceeded. You can increase this limit outside the program. For example, for Mac El Captain and Sierra, the following command raises the limit to 2000.
# view the limits
ulimit -a

# raise the limit to 2000
ulimit -n 2000

Note

  • Note that if the chromosome pair block are ordered in a way that the first coordinate is always smaller than the second ('upper-triangle'), a lower-triangle query will return an empty result. For example, if there is a block with chr1='6' and chr2='X', but not with chr1='X' and chr2='6', then the query for X|6 will not return any result. The search is not symmetric. However, using the -a option for pairix or flip option for pypairix turns on autoflip, which searches for '6|X' if 'X|6' doesn't exist.
  • Tabix and pairix indices are not cross-compatible.

Version history

0.3.7

  • The issue with integer overflow with get_linecount of pypairix is now fixed. (no need to re-index).
  • Fixed issue where autoflip causes segmentation fault or returns an empty result on some systems. This affects pairix -Y, pairix -a, pypairix.check_triangle() and pypairix.querys2D(). It does not affect the results on 4DN Data Portal.

0.3.6

  • Line count (pairix -n) integer overflow issue has been fixed. The index structure has changed. The index generated by the previous versions (0.2.5 ~ 0.3.3, 0.3.4 ~ 0.3.5) can be auto-detected and used as well (backward compatible).

0.3.5

  • Backward compatibility is added - The index generated by the previous version (0.2.5 ~ 0.3.3) can now be auto-detected and used by Pairix.

0.3.4

  • The maximum chromosome size allowed is now 2^30 instead of 2^29 with new index. Index structure changed.

0.3.3

  • The problem of pypairix get_blocknames crashing python when called twice now fixed.

0.3.2

  • pairix -Y option is now available to check whether a pairix-indexed file is a triangle (i.e. a chromosome pair occurs in one direction. e.g. if chr1|chr2 exists, chr2|chr1 doesn't)
  • pypairix check_triangle function is also now available to check whether a pairix-indexed file is a triangle.
  • pairix -B option is now listed as part of the usage.

0.3.1

  • pairix -B option is now available to print out the number of bgzf blocks for each chromosome (pair).
  • The same function is available for pypairix (bgzf_block_count).

0.3.0

  • The problem with fragment_4dnpairs.pl of adding an extra column is now fixed.
  • 1D querying on 2D data now works with pypairix (function querys2D).

0.2.9

  • pairix can now take 1D query for 2D data. e.g.) pairix file.gz 'chr22:50000-60000' is equivalent to pairix file.gz 'chr22:50000-60000|chr22:50000-60000' if file.gz is 2D indexed.

0.2.8

  • pairix now has option -a (autoflip) that flips the query in case the matching chromosome pair doesn't exist in the file.
  • pairix now has option -W that prints out region split character use for indexing a specific file.
  • merge-pairs.sh is now included in util.
  • pairix can now take 1D query for 2D data. e.g.) pairix file.gz 'chr22:50000-60000' is equivalent to pairix file.gz 'chr22:50000-60000|chr22:50000-60000' if file.gz is 2D indexed.  This one currently does not work.

0.2.6

  • Two utils are added: duplicate_header_remover.pl and column_remover.pl for pairs file format correction.

0.2.5

  • pairix has now option -w which specifies region split character (default '|') during indexing. A query string should use this character as a separater.
  • pypairix also now has a parameter region_split_character in function build_index (default '|')
  • juicer_shortform2pairs.pl is now available in the util folder.
  • Index structure changed - please re-index if you're using an older version of index.

0.2.4

  • Updated magic number for the new index, to avoid crash caused by different index structure.

0.2.3

  • Total linecount is added to the index now with virtually no added runtime or memory for indexing (pairix -n and pypairix get_linecount to retrieve the total line count)
  • Index structure changed - please re-index if you're using an older version of index.

0.2.2

  • fixed -s option still not working in old_merged_nodups2pairs.pl.

0.2.1

  • fixed a newly introdued error in fragment_4dnpairs.pl

0.2.0

  • fixed --split option still not working in merged_noduds2pairs.pl and old_merged_nodups2pairs.pl.

0.2.0

  • fixed an issue of not excluding chromosomes that are not in chrome size file in merged_noduds2pairs.pl and old_merged_nodups2pairs.pl
  • fixed --split option not working in merged_noduds2pairs.pl and old_merged_nodups2pairs.pl
  • mapq filtering option (-m|--mapq) is added to merged_noduds2pairs.pl and old_merged_nodups2pairs.pl

0.1.8

  • Now util has an (updated) fragment_4dnpairs.pl script in it, which allows adding juicer fragment index information to 4DN-DCIC style pairs file.

0.1.7

  • Now pairix index contains a pairix-specific magic number that differentiates it from a tabix index.
  • Pypairix produces a better error message when the index file doesn't exist (instead of throwing a segfault).

0.1.6

  • merged_nodup2pairs.pl and old_merged_nodup2pairs.pl now take chromsize file and adds chromsize in the output file header. Upper triangle is also defined according to the chromsize file.
  • bam2pairs: the option description in the usage printed out and the command field in the output pairs file has not been fixed. (-l instead of -5 for the opposite effect)
  • pairix': command pairix --help now exits 0 after printing usage (pairix` alone exits 1 as before).

0.1.5

  • pypairix: function build_index now has option zero which created a zero-based index (defaut 1-based).
  • bam2pairs: now adds chromsize in the header. Optionally takes chromsize file to define mate ordering and filter chromosomes. If chromsize file is not fed, the mate ordering is alphanumeric.
  • pypairix: functions get_header and get_chromsize are added.
  • pairs format now has chromsize in the header as requirement.

0.1.4

  • fixed usage print for merged_nodup2pairs.pl and old_merged_nodup2pairs.pl.
  • pypairix: function exists2 is added

0.1.3

  • added build_index methods. Now you can build index files (.px2) using command line, R, or Python
    • R: px_build_index() : see Rpairix
    • Python: pypairix.build_index()
  • tests updated
  • pairs_format_specification updated

0.1.2

  • Now custom column set overrides file extension recognition
  • bam2pairs now records 5end of a read for position (instead of leftmost)
  • Version number in the binaries fixed.

0.1.1

  • Now all source files are in src/.
  • pypairix: function exists is added
  • pairix: indexing presets (-p option) now includes pairs, merged_nodups, old_merged_nodups. It also automatically recognizes extension .pairs.gz.
  • merged_nodups.tab examples are now deprecated (since the original space-delimited files can be recognized as well)
  • pairs_merger: memory error fixed
  • updated tests

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1D/2D indexing and querying on bgzipped text file with a pair of genomic coordinates

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python c bioinformatics pairs hi-c random-access bgzip pypairix

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Feb 2, 2024
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