Rsamtools 2.15.1
Many users will find that the GenomicAlignments package provides a more useful
representation of BAM files in R; the GenomicFiles package is also useful for
iterating through BAM files.
The Rsamtools package provides an interface to BAM files. BAM files are
produced by samtools and other software, and represent a flexible format for
storing ‘short’ reads aligned to reference genomes. BAM files
typically contain sequence and base qualities, and alignment coordinates
and quality measures. BAM files are appealing for several reasons. The
format is flexible enough to represent reads generated and aligned using
diverse technologies. The files are binary so that file access is
relatively efficient. BAM files can be indexed, allowing ready access
to localized chromosomal regions. BAM files can be accessed remotely,
provided the remote hosting site supports such access and a local index
is available. This means that specific regions of remote files can be
accessed without retrieving the entire (large!) file. A full description
is available in the BAM format specification
(http://samtools.sourceforge.net/SAM1.pdf)
The main purpose of the Rsamtools is to import BAM files into R.Rsamtools also
provides some facility for file access such as record counting, index
file creation, and filtering to create new files containing subsets of
the original. An important use case for Rsamtools is as a starting point for
creating objects suitable for a diversity of work flows, e.g., objects
in the package (for quality assessment and read manipulation), or
objects in package (for RNA-seq and other applications). Those desiring
more functionality are encouraged to explore and related software
efforts.
ScanBamParamThe essential capability provided by Rsamtools is BAM input. This is
accomplished with the scanBam function. scanBam takes as input the name of the BAM
file to be parsed. In addition, the param argument determines which genomic
coordinates of the BAM file, and what components of each record, will
be input. Rparam is an instance of the ScanBamParam class. To create a param object, call ScanBamParam. Here
we create a param object to extract reads aligned to three distinct ranges
(one on seq1, two on seq2). From each of read in those ranges, we specify that
we would like to extract the reference name (rname, e.g., seq1 ), strand,
alignment position, query (i.e., read) width, and query sequence:
which <- GRanges(c(
"seq1:1000-2000",
"seq2:100-1000",
"seq2:1000-2000"
))
## equivalent:
## GRanges(
## seqnames = c("seq1", "seq2", "seq2"),
## ranges = IRanges(
## start = c(1000, 100, 1000),
## end = c(2000, 1000, 2000)
## )
## )
what <- c("rname", "strand", "pos", "qwidth", "seq")
param <- ScanBamParam(which=which, what=what)Additional information can be
found on the help page for ScanBamParam. Reading the relevant records from the BAM
file is accomplished with
bamFile <- system.file("extdata", "ex1.bam", package="Rsamtools")
bam <- scanBam(bamFile, param=param)Like scan, scanBam returns a list of values. Each element of the list corresponds to a
range specified by the which argument to ScanBamParam.
class(bam)## [1] "list"names(bam)## [1] "seq1:1000-2000" "seq2:100-1000" "seq2:1000-2000"Each element is itself a list, containing the elements
specified by the what and tag arguments to ScanBamParam.
class(bam[[1]])## [1] "list"names(bam[[1]])## [1] "rname" "strand" "pos" "qwidth" "seq"The elements are either basic R or IRanges data types
sapply(bam[[1]], class)## rname strand pos qwidth seq
## "factor" "factor" "integer" "integer" "DNAStringSet"A paradigm for collapsing the list-of-lists into a single list is
.unlist <- function (x)
{
## do.call(c, ...) coerces factor to integer, which is undesired
x1 <- x[[1L]]
if (is.factor(x1)) {
structure(unlist(x), class = "factor", levels = levels(x1))
} else {
do.call(c, x)
}
}
bam <- unname(bam) # names not useful in unlisted result
elts <- setNames(bamWhat(param), bamWhat(param))
lst <- lapply(elts, function(elt) .unlist(lapply(bam, "[[", elt)))This might be further transformed, e.g., to a DataFrame, with
head(do.call("DataFrame", lst))## DataFrame with 6 rows and 5 columns
## rname strand pos qwidth seq
## <factor> <factor> <integer> <integer> <DNAStringSet>
## 1 seq1 + 970 35 TATTAGGAAA...ACTATGAAGA
## 2 seq1 + 971 35 ATTAGGAAAT...CTATGAAGAG
## 3 seq1 + 972 35 TTAGGAAATG...TATGAAGAGA
## 4 seq1 + 973 35 TAGGAAATGC...ATGAAGAGAC
## 5 seq1 + 974 35 AGGAAATGCT...TGAAGAGACT
## 6 seq1 - 975 35 GGAAATGCTT...GAAGAGACTAOften, an alternative is to use a ScanBamParam object with desired fields specified in what as an argument to GenomicAlignments::readGAlignments; the specified fields are added as columns to the returned GAlignments
.
BAM index filesThe BAM file in the previous example includes an index, represented by
a separate file with extension .bai:
list.files(dirname(bamFile), pattern="ex1.bam(.bai)?")## [1] "ex1.bam" "ex1.bam.bai"Indexing provides two significant benefits. First, an index allows a BAM file to be efficiently accessed by range. A corollary is that providing a which argument to scanBamPram requires an index. Second, coordinates for extracting
information from a BAM file can be derived from the index, so a
portion of a remote BAM file can be retrieved with local access only to the index. For instance, provided an index file exists on the local computer, it is possible to retrieve a small portion of a BAM file residing on the 1000 genomes HTTP server. The url
ftp://ftp-trace.ncbi.nih.gov/1000genomes/ftp/pilot_data/data/NA19240/alignment/NA19240.chrom6.SLX.maq.SRP000032.2009_07.bam
points to the BAM file corresponding to individual NA19240
chromosome 6 Solexa (Illumina) sequences aligned using MAQ. The remote file is very large (about 10 GB), but the corresponding index file is small (about 500 KB). With na19240url set to the above address, the following retrieves just those reads in the specified range
which <- GRanges("6:100000-110000")
param <- ScanBamParam(which=which, what=scanBamWhat())
na19240bam <- scanBam(na19240url, param=param)Invoking scanBam without an index file, as above, first retrieves the index file from the remote location, and then
queries the remote file using the index; for repeated queries, it is
more efficient to retrieve the index file first (e.g., with download.file) and then use the local index as an argument to scanBam. Many BAM files were created in
a way that causes scanBam to report that the “EOF marker is absent”; this message can safely be ignored.
BAM filesBAM files may be read by functions in packages other than Rsamtools, in particular the readGAlignments family of functions in GenomicAlignments.
Additional ways of interacting with BAM files include scanBamHeader (to extract
header information) and countBam (to count records matching param). filterBam filters reads from
the source file according to the criteria of the ScanBamParam parameter, writing
reads passing the filter to a new file. The function sorts a previously
unsorted BAM, while The function indexBam creates an index file from a sorted BAM file.
readPileup reads a pileup file created by , importing SNP, indel, or all variants
into a GRanges object.
BAM files can be large, containing more information on more genomic
regions than are of immediate interest or than can fit in memory. The first strategy for dealing with this is to select, using the what and which arguments to scanBamParam, just those portions of the BAM file that are essential
to the current analysis, e.g., specifying what=c('rname', 'qname', 'pos') when wishing to calculate coverage of ungapped reads.
When selective input of BAM files is still too memory-intensive, the file can be processed in chunks, with each chunk distilled to the derived information of interest. Chromosomes will often be the natural chunk to process. For instance, here we write a summary function that takes a single sequence name (chromosome) as input, reads in specific information from the BAM file, and calculates coverage over that sequence.
summaryFunction <-
function(seqname, bamFile, ...)
{
param <- ScanBamParam(
what=c('pos', 'qwidth'),
which=GRanges(seqname, IRanges(1, 1e7)),
flag=scanBamFlag(isUnmappedQuery=FALSE)
)
x <- scanBam(bamFile, ..., param=param)[[1]]
coverage(IRanges(x[["pos"]], width=x[["qwidth"]]))
}This might be used as follows; it is an
ideal candidate for evaluation in parallel, e.g., using the parallel package and srapply function in ShortRead.
seqnames <- paste("seq", 1:2, sep="")
cvg <- lapply(seqnames, summaryFunction, bamFile)
names(cvg) <- seqnames
cvg## $seq1
## integer-Rle of length 1569 with 1054 runs
## Lengths: 2 2 1 3 4 2 3 4 2 4 1 ... 1 2 1 1 1 1 1 1 1 1
## Values : 1 2 3 4 5 7 8 9 11 12 13 ... 13 12 10 9 7 6 5 3 2 1
##
## $seq2
## integer-Rle of length 1567 with 1092 runs
## Lengths: 1 3 1 1 1 3 1 4 1 1 6 ... 1 1 1 1 1 2 1 4 4 1
## Values : 3 4 5 8 12 14 15 16 17 18 19 ... 15 14 13 10 8 7 6 3 2 1The result of the function (a coverage vector, in this case) will often be much smaller than the input.
The GenomicFiles package implements strategies for iterating through BAM and other files, including in parallel.
The functions described in the previous section import data in to R. However, sequence data can be very large, and it does not always make sense to read the data in immediately. Instead, it can be useful to marshal references to the data into a container and then act on components of the container. The BamViews class provides a mechanism for creating ‘views’ into a set of BAM files. The view itself is light-weight, containing references to the relevant BAM files and metadata about the
view (e.g., the phenotypic samples corresponding to each BAM file).
One way of understanding a instance is as a rectangular data structure.
The columns represent BAM files (e.g., distinct samples). The rows
represent ranges (i.e., genomic coordinates). For instance, a ChIP-seq
experiment might identify a number of peaks of high read counts.
To illustrate, suppose we have an interest in caffeine metabolism in humans. The ‘rows’ contain coordinates of genomic regions associated with genes in a KEGG caffeine metabolism pathway. The ‘columns’ represent individuals in the 1000 genomes project.
To create the ‘rows’, we identify possible genes that KEGG associates with caffeine metabolism. Using the KEGGREST package, the steps are
## uses KEGGREST, dplyr, and tibble packages
org <- "hsa"
caffeine_pathway <-
KEGGREST::keggList("pathway", org)
tibble::enframe(name = "pathway_id", value = "pathway")
dplyr::filter(startsWith(.data$pathway, "Caffeine metabolism"))
egid <-
KEGGREST::keggLink(org, "pathway") %>%
tibble::enframe(name = "pathway_id", value = "gene_id")
dplyr::left_join(x = caffeine_pathway, by = "pathway_id")
dplyr::mutate(gene_id = sub("hsa:", "", gene_id))
pull(gene_id)At the time of writing, genes in the caffeine metabolism pathway are
egid <- c("10", "1544", "1548", "1549", "7498", "9")Then we use the appropriate TxDb package to
translate Entrez identifiers to obtain ranges of interest (one could also use biomaRt to retrieve coordinates for non-model
organisms, perhaps making a TxDb object as outlined
in the GenomicFeatures vignette). We’ll find that the names
used for chromosomes in the alignments differ from those used at
Ensembl, so seqlevels<- is used to map between naming schemes
and to drop unused levels.
library(TxDb.Hsapiens.UCSC.hg18.knownGene)bamRanges <- transcripts(
TxDb.Hsapiens.UCSC.hg18.knownGene,
filter=list(gene_id=egid)
)
seqlevels(bamRanges) <- # translate seqlevels
sub("chr", "", seqlevels(bamRanges))
lvls <- seqlevels(bamRanges) # drop unused levels
seqlevels(bamRanges) <- lvls[lvls %in% as.character(seqnames(bamRanges))]
bamRanges## GRanges object with 18 ranges and 2 metadata columns:
## seqnames ranges strand | tx_id tx_name
## <Rle> <IRanges> <Rle> | <integer> <character>
## [1] 2 31410692-31491115 - | 9095 uc002rnv.1
## [2] 8 18111895-18125100 + | 26333 uc003wyq.1
## [3] 8 18111895-18125100 + | 26334 uc003wyr.1
## [4] 8 18111895-18125100 + | 26335 uc003wys.1
## [5] 8 18113074-18125100 + | 26336 uc003wyt.1
## ... ... ... ... . ... ...
## [14] 19 46042667-46048192 - | 57448 uc010ehe.1
## [15] 19 46043701-46048191 - | 57449 uc010ehf.1
## [16] 19 46073184-46080497 - | 57450 uc002opm.1
## [17] 19 46073184-46080497 - | 57451 uc002opn.1
## [18] 19 46073184-46226008 - | 57452 uc002opo.1
## -------
## seqinfo: 4 sequences from hg18 genomeThe bamRanges ‘knows’ the genome for which the ranges are
defined
unique(genome(bamRanges))## [1] "hg18"Here we retrieve a vector of BAM file URLs (slxMaq09)
from the package.
slxMaq09 <- local({
fl <- system.file("extdata", "slxMaq09_urls.txt", package="Rsamtools")
readLines(fl)
})We now assemble the BamViews instance from these objects; we
also provide information to annotated the BAM files (with the
bamSamples function argument, which is a DataFrame
instance with each row corresponding to a BAM file) and the
instance as a whole (with bamExperiment, a simple named
list containing information structured as the user sees fit).
bamExperiment <-
list(description="Caffeine metabolism views on 1000 genomes samples",
created=date())
bv <- BamViews(
slxMaq09, bamRanges=bamRanges, bamExperiment=bamExperiment
)
metadata(bamSamples(bv)) <-
list(description="Solexa/MAQ samples, August 2009",
created="Thu Mar 25 14:08:42 2010")
bv## BamViews dim: 18 ranges x 24 samples
## names: NA06986.SLX.maq.SRP000031.2009_08.bam NA06994.SLX.maq.SRP000031.2009_08.bam ... NA12828.SLX.maq.SRP000031.2009_08.bam NA12878.SLX.maq.SRP000031.2009_08.bam
## detail: use bamPaths(), bamSamples(), bamRanges(), ...The BamViews object can be queried for its component parts, e.g.,
bamExperiment(bv)## $description
## [1] "Caffeine metabolism views on 1000 genomes samples"
##
## $created
## [1] "Wed Mar 15 15:28:33 2023"More usefully, methods in Rsamtools are designed to work with BamViews objects, retrieving data from all files in the view. These operations can take substantial time and require reliable network access.
To illustrate, the following code (not evaluated when this vignette was created) downloads the index files associated with the bv object
bamIndexDir <- tempfile()
indexFiles <- paste(bamPaths(bv), "bai", sep=".")
dir.create(bamIndexDir)
bv <- BamViews(
slxMaq09,
file.path(bamIndexDir, basename(indexFiles)), # index file location
bamRanges=bamRanges,
bamExperiment=bamExperiment
)
idxFiles <- mapply(
download.file, indexFiles,
bamIndicies(bv),
MoreArgs=list(method="curl")
)and then queries the 1000 genomes project for reads overlapping our transcripts.
library(GenomicAlignments)
olaps <- readGAlignments(bv)The resulting object is about 11 MB in size. To avoid having to download this data each time the vignette is run, we instead load it from disk
load(system.file("extdata", "olaps.Rda", package="Rsamtools"))
olaps## List of length 24
## names(24): NA06986.SLX.maq.SRP000031.2009_08.bam ...head(olaps[[1]])## GAlignments object with 6 alignments and 0 metadata columns:
## seqnames strand cigar qwidth start end width
## <Rle> <Rle> <character> <integer> <integer> <integer> <integer>
## [1] 2 + 51M 51 31410650 31410700 51
## [2] 2 + 51M 51 31410658 31410708 51
## [3] 2 - 51M 51 31410663 31410713 51
## [4] 2 + 51M 51 31410666 31410716 51
## [5] 2 - 51M 51 31410676 31410726 51
## [6] 2 + 51M 51 31410676 31410726 51
## njunc
## <integer>
## [1] 0
## [2] 0
## [3] 0
## [4] 0
## [5] 0
## [6] 0
## -------
## seqinfo: 114 sequences from an unspecified genomeThere are 33964 reads in NA06986.SLX.maq.SRP000031.2009_08.bam overlapping at least one of our transcripts. It is easy to explore this object, for instance discovering the range of read widths in each individual.
head(t(sapply(olaps, function(elt) range(qwidth(elt)))))## [,1] [,2]
## NA06986.SLX.maq.SRP000031.2009_08.bam 51 51
## NA06994.SLX.maq.SRP000031.2009_08.bam 36 51
## NA07051.SLX.maq.SRP000031.2009_08.bam 51 51
## NA07346.SLX.maq.SRP000031.2009_08.bam 48 76
## NA07347.SLX.maq.SRP000031.2009_08.bam 51 51
## NA10847.SLX.maq.SRP000031.2009_08.bam 36 51Suppose we were particularly interested in the first transcript, which
has a transcript id
uc002rnv.1. Here we
extract reads overlapping this transcript from each of our samples. As
a consequence of the protocol used, reads aligning to either strand
could be derived from this transcript. For this reason, we set the
strand of our range of interest to *. We use the
endoapply function, which is like lapply but
returns an object of the same class (in this case,
SimpleList) as its first argument.
rng <- bamRanges(bv)[1]
strand(rng) <- "*"
olap1 <- endoapply(olaps, subsetByOverlaps, rng)
olap1 <- lapply(olap1, "seqlevels<-", value=as.character(seqnames(rng)))
head(olap1[[24]])## GAlignments object with 6 alignments and 0 metadata columns:
## seqnames strand cigar qwidth start end width
## <Rle> <Rle> <character> <integer> <integer> <integer> <integer>
## [1] 2 + 36M 36 31410660 31410695 36
## [2] 2 - 36M 36 31410670 31410705 36
## [3] 2 + 36M 36 31410683 31410718 36
## [4] 2 - 36M 36 31410687 31410722 36
## [5] 2 - 36M 36 31410694 31410729 36
## [6] 2 - 36M 36 31410701 31410736 36
## njunc
## <integer>
## [1] 0
## [2] 0
## [3] 0
## [4] 0
## [5] 0
## [6] 0
## -------
## seqinfo: 1 sequence from an unspecified genomeTo carry the example a little further, we calculate coverage of each sample:
minw <- min(sapply(olap1, function(elt) min(start(elt))))
maxw <- max(sapply(olap1, function(elt) max(end(elt))))
cvg <- endoapply(
olap1, coverage,
shift=-start(ranges(bamRanges[1])),
width=width(ranges(bamRanges[1]))
)
cvg[[1]]## RleList of length 1
## $`2`
## integer-Rle of length 80424 with 13290 runs
## Lengths: 8 8 5 2 1 3 7 7 10 2 3 ... 4 3 1 11 8 7 17 4 4 9
## Values : 6 5 4 3 4 3 5 3 4 5 6 ... 4 5 4 5 4 5 4 3 2 1Since the example includes a single region of uniform width across all samples, we can easily create a coverage matrix with rows representing nucleotide and columns sample and, e.g., document variability between samples and nucleotides
m <- matrix(unlist(lapply(cvg, lapply, as.vector)), ncol=length(cvg))
summary(rowSums(m))## Min. 1st Qu. Median Mean 3rd Qu. Max.
## 10.00 74.00 82.00 81.63 91.00 133.00summary(colSums(m))## Min. 1st Qu. Median Mean 3rd Qu. Max.
## 133924 173925 248333 273528 350823 567727This vignette has summarized facilities in the Rsamtools package. Important additional packages include GenomicRanges
(for representing and manipulating gapped alignments),
ShortRead for I/O and quality assessment of ungapped short
read alignments, Biostrings and BSgenome for DNA
sequence and whole-genome manipulation, IRanges for
range-based manipulation, and rtracklayer for I/O related
to the UCSC genome browser. Users might also find the interface to the
integrative genome browser (IGV) in SRAdb useful for
visualizing BAM files.
packageDescription("Rsamtools")## Package: Rsamtools
## Type: Package
## Title: Binary alignment (BAM), FASTA, variant call (BCF), and tabix
## file import
## Description: This package provides an interface to the 'samtools',
## 'bcftools', and 'tabix' utilities for manipulating SAM
## (Sequence Alignment / Map), FASTA, binary variant call (BCF)
## and compressed indexed tab-delimited (tabix) files.
## biocViews: DataImport, Sequencing, Coverage, Alignment, QualityControl
## URL: https://bioconductor.org/packages/Rsamtools
## Video:
## https://www.youtube.com/watch?v=Rfon-DQYbWA&list=UUqaMSQd_h-2EDGsU6WDiX0Q
## BugReports: https://github.com/Bioconductor/Rsamtools/issues
## Version: 2.15.1
## License: Artistic-2.0 | file LICENSE
## Encoding: UTF-8
## Author: Martin Morgan, Hervé Pagès, Valerie Obenchain, Nathaniel Hayden
## Maintainer: Bioconductor Package Maintainer
## <maintainer@bioconductor.org>
## Depends: methods, GenomeInfoDb (>= 1.1.3), GenomicRanges (>= 1.31.8),
## Biostrings (>= 2.47.6), R (>= 3.5.0)
## Imports: utils, BiocGenerics (>= 0.25.1), S4Vectors (>= 0.17.25),
## IRanges (>= 2.13.12), XVector (>= 0.19.7), zlibbioc, bitops,
## BiocParallel, stats
## Suggests: GenomicAlignments, ShortRead (>= 1.19.10), GenomicFeatures,
## TxDb.Dmelanogaster.UCSC.dm3.ensGene,
## TxDb.Hsapiens.UCSC.hg18.knownGene, RNAseqData.HNRNPC.bam.chr14,
## BSgenome.Hsapiens.UCSC.hg19, RUnit, BiocStyle
## LinkingTo: Rhtslib (>= 1.99.3), S4Vectors, IRanges, XVector, Biostrings
## LazyLoad: yes
## SystemRequirements: GNU make
## git_url: https://git.bioconductor.org/packages/Rsamtools
## git_branch: master
## git_last_commit: 1f65f29
## git_last_commit_date: 2022-12-30
## Date/Publication: 2022-12-30
## NeedsCompilation: yes
## Packaged: 2022-12-31 02:26:06 UTC; biocbuild
## Built: R 4.3.0; x86_64-w64-mingw32; 2022-12-31 14:41:41 UTC; windows
## Archs: x64
##
## -- File: C:/Program Files/R/R-devel/library/Rsamtools/Meta/package.rdssessionInfo()## R Under development (unstable) (2023-03-14 r83979 ucrt)
## Platform: x86_64-w64-mingw32/x64 (64-bit)
## Running under: Windows 10 x64 (build 19042)
##
## Matrix products: default
##
##
## locale:
## [1] LC_COLLATE=English_United States.utf8
## [2] LC_CTYPE=English_United States.utf8
## [3] LC_MONETARY=English_United States.utf8
## [4] LC_NUMERIC=C
## [5] LC_TIME=English_United States.utf8
##
## time zone: Africa/Lagos
## tzcode source: internal
##
## attached base packages:
## [1] stats4 stats graphics grDevices utils datasets methods
## [8] base
##
## other attached packages:
## [1] GenomicAlignments_1.35.1
## [2] SummarizedExperiment_1.29.1
## [3] MatrixGenerics_1.11.0
## [4] matrixStats_0.63.0
## [5] TxDb.Hsapiens.UCSC.hg18.knownGene_3.2.2
## [6] GenomicFeatures_1.51.4
## [7] AnnotationDbi_1.61.2
## [8] Biobase_2.59.0
## [9] Rsamtools_2.15.1
## [10] Biostrings_2.67.0
## [11] XVector_0.39.0
## [12] GenomicRanges_1.51.4
## [13] GenomeInfoDb_1.35.15
## [14] IRanges_2.33.0
## [15] S4Vectors_0.37.4
## [16] BiocGenerics_0.45.0
## [17] BiocStyle_2.27.1
##
## loaded via a namespace (and not attached):
## [1] tidyselect_1.2.0 dplyr_1.1.0 blob_1.2.3
## [4] filelock_1.0.2 bitops_1.0-7 fastmap_1.1.1
## [7] RCurl_1.98-1.10 BiocFileCache_2.7.2 XML_3.99-0.13
## [10] digest_0.6.31 lifecycle_1.0.3 ellipsis_0.3.2
## [13] KEGGREST_1.39.0 RSQLite_2.3.0 magrittr_2.0.3
## [16] compiler_4.3.0 rlang_1.1.0 sass_0.4.5
## [19] progress_1.2.2 tools_4.3.0 utf8_1.2.3
## [22] yaml_2.3.7 rtracklayer_1.59.1 knitr_1.42
## [25] prettyunits_1.1.1 bit_4.0.5 curl_5.0.0
## [28] DelayedArray_0.25.0 xml2_1.3.3 BiocParallel_1.33.9
## [31] grid_4.3.0 fansi_1.0.4 biomaRt_2.55.0
## [34] cli_3.6.0 rmarkdown_2.20 crayon_1.5.2
## [37] generics_0.1.3 rstudioapi_0.14 httr_1.4.5
## [40] rjson_0.2.21 DBI_1.1.3 cachem_1.0.7
## [43] stringr_1.5.0 zlibbioc_1.45.0 parallel_4.3.0
## [46] BiocManager_1.30.20 restfulr_0.0.15 vctrs_0.5.2
## [49] Matrix_1.5-3 jsonlite_1.8.4 bookdown_0.33
## [52] hms_1.1.2 bit64_4.0.5 jquerylib_0.1.4
## [55] glue_1.6.2 codetools_0.2-19 stringi_1.7.12
## [58] BiocIO_1.9.2 tibble_3.2.0 pillar_1.8.1
## [61] rappdirs_0.3.3 htmltools_0.5.4 GenomeInfoDbData_1.2.9
## [64] R6_2.5.1 dbplyr_2.3.1 lattice_0.20-45
## [67] evaluate_0.20 png_0.1-8 memoise_2.0.1
## [70] bslib_0.4.2 Rcpp_1.0.10 xfun_0.37
## [73] pkgconfig_2.0.3Note: The following operations were performed at the time the
vignette was written; location of on-line resources, in particular the
organization of the 1000 genomes BAM files, may have changed.
We are interested in collecting the URLs of a number of BAM files
from the 1000 genomes project. Our first goal is to identify files
that might make for an interesting comparison. First, let’s visit the
1000 genomes FTP site and discover available files. We’ll use the
RCurl package to retrieve the names of all files in an
appropriate directory
library(RCurl)
ftpBase <-
"ftp://ftp-trace.ncbi.nih.gov/1000genomes/ftp/pilot_data/data/"
indivDirs <-
strsplit(getURL(ftpBase, ftplistonly=TRUE), "\n")[[1]]
alnDirs <-
paste(ftpBase, indivDirs, "/alignment/", sep="")
urls0 <-
strsplit(getURL(alnDirs, dirlistonly=TRUE), "\n")From these, we exclude directories without any files in them, select
only the BAM index (extension .bai) files, and choose those
files that exactly six '.' characters in their name.
urls <- urls[sapply(urls0, length) != 0]
fls0 <- unlist(unname(urls0))
fls1 <- fls0[grepl("bai$", fls0)]
fls <- fls1[sapply(strsplit(fls1, "\\."), length)==7]After a little exploration, we focus on those files
obtained form Solexa sequencing, aligned using MAQ, and archived in
August, 2009; we remove the .bai extension, so that the URL refers to the underlying file rather than index. There are 24 files.
urls1 <- Filter(
function(x) length(x) != 0,
lapply(urls, function(x) x[grepl("SLX.maq.*2009_08.*bai$", x)])
)
slxMaq09.bai <-
mapply(paste, names(urls1), urls1, sep="", USE.NAMES=FALSE)
slxMaq09 <- sub(".bai$", "", slxMaq09.bai)As a final step to prepare for using a file, we create local copies of the index files. The index files are relatively small (about 190 Mb total).
bamIndexDir <- tempfile()
dir.create(bamIndexDir)
idxFiles <- mapply(
download.file, slxMaq09.bai,
file.path(bamIndexDir, basename(slxMaq09.bai)) ,
MoreArgs=list(method="curl")
)