[BioC] Filtering BAM files by start position for VariantTools
Valerie Obenchain
vobencha at fhcrc.org
Thu Jul 11 22:11:46 CEST 2013
As an fyi, Martin just checked in a change to Rsamtools (devel) that
allows filtering by range. This should speed up the filtering
substantially. I'll use the new syntax in the filter example below.
I'm not sure of the best way to tallyVariants for all groups of reads
for each unique start position. Here's an approach I might take - maybe
others will chime in with their ideas. Start by reading in the bam and
identify the unique starts.
library(Rsamtools)
fl <- system.file("extdata", "ex1.bam", package="Rsamtools")
gal <- readGAlignments(fl)
starts <- unique(start(gal))
mclapply() over the seqlevels containing unique starts.
(code not tested)
lst <- split(start(gal), as.factor(seqnames(gal)))
starts <- lapply(lst, unique)
vtparam <- VariantTallyParam(...)
mclapply(starts,
function(start, rname, fl, vtparam) {
## 'what' imports only the fields used in the filter
## 'which' is the position(s) to overlap
param <- ScanBamParam(
what=c("rname", "pos"),
which=GRanges(rname,
IRanges(start, width=1)))
filter <- FilterRules(list(atPos = function(x) {
(x$rname %in% rname) &
(x$pos %in% start)}))
dest0 <- filterBam(fl, tempfile(),
filter=filter, param=param)
tallyVariants(dest0, vtparam)},
rname=names(starts), fl=fl, vtparam=vtparam)
Rsamtools in devel is broken today but should be ok tomorrow.
Valerie
On 07/11/2013 10:27 AM, Taylor, Sean D wrote:
> Thanks Valerie, I'll give that a try. And I see that you just clarified my question about the input file for tallyVariants.
>
> I had thought about doing this before but hadn't been able to figure out the proper filter syntax. Thanks! The only downside to this approach is that I ultimately want to do this for all unique start sites that align to my reference. That could entail generating thousands of tempfiles that all have to be read back in. It could be done with lapply, but it sounds rather memory and time intensive. Another approach that I tried was reading the bam file as a GappedAlignments object and then splitting it by start position into a GAlignmentsList. That was really easy, but so far as I can tell tallyVariants will not accept GappedAlignments objects as an input. I wonder if there is another way to vectorize this approach?
>
> Thanks,
> Sean
>
>
> -----Original Message-----
> From: Valerie Obenchain [mailto:vobencha at fhcrc.org]
> Sent: Thursday, July 11, 2013 10:02 AM
> To: Taylor, Sean D
> Cc: bioconductor at r-project.org; Michael Lawrence
> Subject: Re: [BioC] Filtering BAM files by start position for VariantTools
>
> Hi Sean,
>
> As you've discovered, the 'which' in the 'param' (for reading bam files) specifies positions to overlap, not start or end. One approach to isolating reads with a specific starting position would be to filter the bam by 'pos'.
>
> library(VariantTools)
> fl <- LungCancerLines::LungCancerBamFiles()$H1993
>
> mystart <- 1110426
> filt <- list(setStart=function(x) x$pos %in% mystart)
> dest <- tempfile()
> filterBam(fl, dest, filter=FilterRules(filt))
> scn <- scanBam(dest)
>
> Confirm all reads start with 'mystart':
>
> > table(scn[[1]]$pos)
>
> 1110426
> 2388
>
> If you want a tally of all nucleotides for all sequences starting with 'mystart' then no need to supply a 'which':
> param <- VariantTallyParam(gmapR::TP53Genome(),
> readlen=100L,
> high_base_quality=23L)
> tally <- tallyVariants(fl, param)
>
>
> Valerie
>
>
> On 07/09/2013 02:06 PM, Taylor, Sean D wrote:
>> I am trying to read a specific set of records from a bam file for use in the VariantTools package. I'm trying to construct a which argument (a GRanges object) that will pull in a set of records from all reads that only start at a specified position. (i.e. all reads that start at position 100). So far I have only been able to specify reads that overlap position 100, but have not been able to find a way to define the start site.
>>
>> #Example code:
>>> bams <- LungCancerLines::LungCancerBamFiles()
>>> bam <- bams$H1993
>>> which<-GRanges(seqnames=c('TP53'), IRanges(1110426, width=1), '+')
>>> tally.param <- VariantTallyParam(gmapR::TP53Genome(),
>> + readlen = 100L,
>> + high_base_quality = 23L,
>> + which = which)
>>> raw.variants <- tallyVariants(bam, tally.param)
>>
>> This code shows all the variants at position 1110426, but not all the variants from the reads that start at position 1110426.
>>
>> Ultimately, I am trying to do this for all start positions in my data set, so I would want something that looks like this pseudocode:
>>> raw.variants<-lapply (start(bam), function (x){
>> which<-GRanges(seqnames=c('chrM'), '+', start=x)
>> tally.param<-VariantTallyParam(gmap, readlen=100L, which=which)
>> tallyVariants(bamfile, tally.param)
>> })
>>
>> Thanks,
>> Sean
>>
>>> sessionInfo()
>> R version 3.0.1 (2013-05-16)
>> Platform: x86_64-unknown-linux-gnu (64-bit)
>>
>> locale:
>> [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=en_US.UTF-8
>> [4] LC_COLLATE=en_US.UTF-8 LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
>> [7] LC_PAPER=C LC_NAME=C LC_ADDRESS=C
>> [10] LC_TELEPHONE=C LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>>
>> attached base packages:
>> [1] grid parallel stats graphics grDevices utils datasets methods base
>>
>> other attached packages:
>> [1] RSQLite_0.11.4 DBI_0.2-7 BiocInstaller_1.10.2
>> [4] LungCancerLines_0.0.8 GenomicFeatures_1.12.1 AnnotationDbi_1.22.5
>> [7] Biobase_2.20.0 gmapR_1.2.0 latticeExtra_0.6-24
>> [10] lattice_0.20-15 RColorBrewer_1.0-5 genoPlotR_0.8
>> [13] ade4_1.5-2 VariantTools_1.2.2 VariantAnnotation_1.6.6
>> [16] Rsamtools_1.12.3 Biostrings_2.28.0 GenomicRanges_1.12.4
>> [19] IRanges_1.18.1 BiocGenerics_0.6.0
>>
>> loaded via a namespace (and not attached):
>> [1] biomaRt_2.16.0 bitops_1.0-5
>> [3] BSgenome_1.28.0 BSgenome.Hsapiens.UCSC.hg19_1.3.19
>> [5] graph_1.38.2 Matrix_1.0-12
>> [7] org.Hs.eg.db_2.9.0 RBGL_1.36.2
>> [9] RCurl_1.95-4.1 rtracklayer_1.20.2
>> [11] stats4_3.0.1 tools_3.0.1
>> [13] TxDb.Hsapiens.UCSC.hg19.knownGene_2.9.2 XML_3.96-1.1
>> [15] zlibbioc_1.6.0
>>
>>
>> [[alternative HTML version deleted]]
>>
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