R: Apply a user-provided function to calculate pile-up...

applyPileups {Rsamtools}

R Documentation

Apply a user-provided function to calculate pile-up statistics across multiple BAM files.

Description

applyPileups scans one or more BAM files, returning position-specific sequence and quality summaries.

Usage

applyPileups(files, FUN, ..., param)

Arguments

`files`	A `PileupFiles` instances.
`FUN`	A function of 1 argument, `x`, to be evaluated for each yield (see `yieldSize`, `yieldBy`, `yieldAll`). The argument `x` is a `list`, with elements describing the current pile-up. The elements of the list are determined by the argument `what`, and include: seqnames: (Always returned) A named `integer()` representing the seqnames corresponding to each position reported in the pile-up. This is a run-length encoding, where the names of the elements represent the seqnames, and the values the number of successive positions corresponding to that seqname. pos: Always returned) A `integer()` representing the genomic coordinate of each pile-up position. seq: An `array` of dimensions nucleotide x file x position. The ‘nucleotide’ dimension is length 5, corresponding to ‘A’, ‘C’, ‘G’, ‘T’, and ‘N’ respectively. Entries in the array represent the number of times the nucleotide occurred in reads in the file overlapping the position. qual: Like `seq`, but summarizing quality; the first dimension is the Phred-encoded quality score, ranging from ‘!’ (0) to ‘~’ (93).
`...`	Additional arguments, passed to methods.
`param`	An instance of the object returned by `ApplyPileupsParam`.

Details

Regardless of param values, the algorithm follows samtools by excluding reads flagged as unmapped, secondary, duplicate, or failing quality control.

Value

applyPileups returns a list equal in length to the number of times FUN has been called, with each element containing the result of FUN.

ApplyPileupsParam returns an object describing the parameters.

Author(s)

Martin Morgan

References

http://samtools.sourceforge.net/

Examples

## The examples below are currently broken and have been disabled for now
## Not run: 
fl <- system.file("extdata", "ex1.bam", package="Rsamtools",
                  mustWork=TRUE)

fls <- PileupFiles(c(fl, fl))

calcInfo <-
    function(x)
{
    ## information at each pile-up position
    info <- apply(x[["seq"]], 2, function(y) {
        y <- y[c("A", "C", "G", "T"),,drop=FALSE]
        y <- y + 1L                     # continuity
        cvg <- colSums(y)
        p <- y / cvg[col(y)]
        h <- -colSums(p * log(p))
        ifelse(cvg == 4L, NA, h)
    })
    list(seqnames=x[["seqnames"]], pos=x[["pos"]], info=info)
}
which <- GRanges(c("seq1", "seq2"), IRanges(c(1000, 1000), 2000))
param <- ApplyPileupsParam(which=which, what="seq")
res <- applyPileups(fls, calcInfo, param=param)
str(res)
head(res[[1]][["pos"]])		# positions matching param
head(res[[1]][["info"]])		# inforamtion in each file

## 'param' as part of 'files'
fls1 <- PileupFiles(c(fl, fl), param=param)
res1 <- applyPileups(fls1, calcInfo)
identical(res, res1)

## yield by position, across ranges
param <- ApplyPileupsParam(which=which, yieldSize=500L,
                           yieldBy="position", what="seq")
res <- applyPileups(fls, calcInfo, param=param)
sapply(res, "[[", "seqnames")

## End(Not run)

[Package Rsamtools version 2.4.0 Index]