R/segmentationPSCBS.R

In PureCN: Copy number calling and SNV classification using targeted short read sequencing

#' PSCBS segmentation
#' 
#' Alternative segmentation function using the \code{PSCBS} package.  This
#' function is called via the \code{fun.segmentation} argument of
#' \code{\link{runAbsoluteCN}}.  The arguments are passed via
#' \code{args.segmentation}.
#' 
#' 
#' @param normal Coverage data for normal sample.
#' @param tumor Coverage data for tumor sample.
#' @param log.ratio Copy number log-ratios, one for each exon in coverage file.
#' @param seg If segmentation was provided by the user, this data structure
#' will contain this segmentation. Useful for minimal segmentation functions.
#' Otherwise PureCN will re-segment the data. This segmentation function
#' ignores this user provided segmentation.
#' @param plot.cnv Segmentation plots.
#' @param sampleid Sample id, used in output files.
#' @param weight.flag.pvalue Flag values with one-sided p-value smaller than
#' this cutoff.
#' @param alpha Alpha value for CBS, see documentation for the \code{segment}
#' function.
#' @param undo.SD \code{undo.SD} for CBS, see documentation of the
#' \code{segment} function. If \code{NULL}, try to find a sensible default.
#' @param flavor Flavor value for PSCBS. See \code{segmentByNonPairedPSCBS}.
#' @param tauA tauA argument for PSCBS. See \code{segmentByNonPairedPSCBS}.
#' @param vcf Optional VCF object with germline allelic ratios.
#' @param tumor.id.in.vcf Id of tumor in case multiple samples are stored in
#' VCF.
#' @param normal.id.in.vcf Id of normal in in VCF. If \code{NULL}, 
#' use unpaired PSCBS.
#' @param max.segments If not \code{NULL}, try a higher \code{undo.SD} 
#' parameter if number of segments exceeds the threshold.
#' @param boost.on.target.max.size When off-target regions are noisy
#' compared to on-target, try to find small segments of specified
#' maximum size that might be missed to due the increased noise.
#' Set to 0 to turn boosting off.
#' @param prune.hclust.h Height in the \code{hclust} pruning step. Increasing
#' this value will merge segments more aggressively. If \code{NULL}, try to 
#' find a sensible default.
#' @param prune.hclust.method Cluster method used in the \code{hclust} pruning
#' step. See documentation for the \code{hclust} function.
#' @param chr.hash Mapping of non-numerical chromsome names to numerical names
#' (e.g. chr1 to 1, chr2 to 2, etc.). If \code{NULL}, assume chromsomes are 
#' properly ordered.
#' @param centromeres A \code{GRanges} with centromere positions.
#' If not \code{NULL}, add breakpoints at centromeres. 
#' @param \dots Additional parameters passed to the 
#' \code{segmentByNonPairedPSCBS} function.
#' @return \code{data.frame} containing the segmentation.
#' @author Markus Riester
#' @references Olshen, A. B., Venkatraman, E. S., Lucito, R., Wigler, M. 
#' (2004). Circular binary segmentation for the analysis of array-based DNA 
#' copy number data. Biostatistics 5: 557-572.
#'
#' Venkatraman, E. S., Olshen, A. B. (2007). A faster circular binary 
#' segmentation algorithm for the analysis of array CGH data. Bioinformatics 
#' 23: 657-63.
#'
#' Olshen et al. (2011). Parent-specific copy number in paired tumor-normal 
#' studies using circular binary segmentation. Bioinformatics.
#' @seealso \code{\link{runAbsoluteCN}}
#' @examples
#' 
#' normal.coverage.file <- system.file("extdata", "example_normal_tiny.txt", 
#'     package="PureCN")
#' tumor.coverage.file <- system.file("extdata", "example_tumor_tiny.txt", 
#'     package="PureCN")
#' vcf.file <- system.file("extdata", "example.vcf.gz",
#'     package="PureCN")
#' 
#' # The max.candidate.solutions, max.ploidy and test.purity parameters are set to
#' # non-default values to speed-up this example.  This is not a good idea for real
#' # samples.
#'  ret <-runAbsoluteCN(normal.coverage.file=normal.coverage.file, 
#'      tumor.coverage.file=tumor.coverage.file, vcf.file=vcf.file, 
#'      sampleid="Sample1",  genome="hg19",
#'      fun.segmentation=segmentationPSCBS, max.ploidy=4,
#'      test.purity=seq(0.3,0.7,by=0.05), max.candidate.solutions=1)
#' 
#' @export segmentationPSCBS
segmentationPSCBS <- function(normal, tumor, log.ratio, seg, plot.cnv, 
    sampleid, weight.flag.pvalue = 0.01, alpha = 0.005, 
    undo.SD = NULL, flavor = "tcn&dh", tauA = 0.03, vcf = NULL,
    tumor.id.in.vcf = 1, normal.id.in.vcf = NULL, max.segments = NULL,
    boost.on.target.max.size = 30,
    prune.hclust.h = NULL, prune.hclust.method = "ward.D", chr.hash = NULL,
    centromeres = NULL, ...) {

    if (!requireNamespace("PSCBS", quietly = TRUE)) {
        .stopUserError("segmentationPSCBS requires the PSCBS package.")
    }

    if (is.null(chr.hash)) chr.hash <- .getChrHash(seqlevels(tumor))
    
    use.weights <- FALSE
    if (!is.null(tumor$weights) && length(unique(tumor$weights)) > 1 ) {
        flog.info("Interval weights found, will use weighted PSCBS.")
        use.weights <- TRUE
    }
    input <- .PSCBSinput(tumor, log.ratio, vcf, tumor.id.in.vcf, 
                         normal.id.in.vcf, chr.hash)

    knownSegmentsCentromeres <- .PSCBSgetKnownSegments(centromeres, chr.hash)

    if (is.null(undo.SD)) undo.SD <- .getSDundo(log.ratio)

    try.again <- 0
    while (try.again < 2) {
        flog.info("Setting undo.SD parameter to %f.", undo.SD)
        knownSegments <- knownSegmentsCentromeres
        if (any(!input$on.target) &&
            boost.on.target.max.size > 0 &&
            .robustSd(input$CT[input$on.target]) * 1.5 < 
            .robustSd(input$CT[!input$on.target])) {
            flog.info("On-target much cleaner than off-target, finding on-target breakpoints first...")
            idxot <- input$on.target
            if (use.weights) {
                idxot <- input$on.target & input$weights >= median(input$weights, na.rm = TRUE)
            }    
            segPSCBSot <- PSCBS::segmentByNonPairedPSCBS(input[idxot,], tauA=tauA, 
                flavor=flavor, undoTCN=undo.SD, knownSegments=knownSegments, 
                min.width=3,alphaTCN=alpha/2, ...)
            segot <- .PSCBSoutput2DNAcopy(segPSCBSot, sampleid)
            if (!is.null(vcf)) {
                segot <- .pruneByHclust(segot, vcf, tumor.id.in.vcf, h=prune.hclust.h, 
                    method=prune.hclust.method, chr.hash=chr.hash)
            }
            segot <- segot[segot$num.mark > 3 & 
                           segot$num.mark <= boost.on.target.max.size, 2:4]
            colnames(segot) <- colnames(knownSegments)[1:3]
            knownSegments <- .PSCBSgetKnownSegments(centromeres, chr.hash, segot)
        }    
        segPSCBS <- PSCBS::segmentByNonPairedPSCBS(input, tauA=tauA, 
            flavor=flavor, undoTCN=undo.SD, knownSegments=knownSegments, 
            min.width=3,alphaTCN=alpha, ...)
        try(flog.debug("Kappa: %f", PSCBS::estimateKappa(segPSCBS)), silent = TRUE)
        seg <- .PSCBSoutput2DNAcopy(segPSCBS, sampleid)
        if (undo.SD <= 0 || is.null(max.segments) || nrow(seg) < max.segments) break
        flog.info("Found %i segments, exceeding max.segments threshold of %i.",
            nrow(seg), max.segments)    
        undo.SD <- undo.SD * 1.5
        try.again <- try.again + 1
    }

    if (plot.cnv) PSCBS::plotTracks(segPSCBS)
    segPSCBS <- NULL

    if (!is.null(vcf)) {
        seg <- .pruneByHclust(seg, vcf, tumor.id.in.vcf, h=prune.hclust.h, 
            method=prune.hclust.method, chr.hash=chr.hash)
    }
    seg <- .addAverageWeights(seg, weight.flag.pvalue, tumor, chr.hash)
    seg
}

.PSCBSinput <- function(tumor, log.ratio, vcf, tumor.id.in.vcf, 
                        normal.id.in.vcf, chr.hash) {
    if (is.null(tumor$weights)) tumor$weights <- 1
    ov <- findOverlaps(vcf, tumor)
    d.f <- cbind(as.data.frame(tumor[subjectHits(ov)]), 
        CT = 2 ^ (log.ratio+1)[subjectHits(ov)], 
        betaT = unlist(geno(vcf[queryHits(ov)])$FA[,tumor.id.in.vcf]), 
        betaN = NA,
        x = start(vcf[queryHits(ov)]),
        w = tumor$weights[subjectHits(ov)])
    
    if (!is.null(normal.id.in.vcf)) {
        d.f$betaN <- unlist(geno(vcf[queryHits(ov)])$FA[,normal.id.in.vcf])
    }

    d.f.2 <- cbind(as.data.frame(tumor[-subjectHits(ov)]), 
        CT = 2 ^ (log.ratio+1)[-subjectHits(ov)], betaT=NA, betaN=NA,
        x = start(tumor[-subjectHits(ov)]),
        w = tumor$weights[-subjectHits(ov)])
    
    d.f <- rbind(d.f, d.f.2)
    colnames(d.f)[1] <- "chromosome"
    d.f <- d.f[order(.strip.chr.name(d.f[,1], chr.hash), d.f$x),]
    d.f$chromosome <- .strip.chr.name(d.f$chromosome, chr.hash)

    if (min(tumor$weights) == max(tumor$weights)) {
        flog.info("Using unweighted PSCBS.")
        d.f$w <- NULL
    }
    d.f
}

.PSCBSgetKnownSegments <- function(centromeres, chr.hash, breakpoints = NULL) {
    if (is.null(centromeres)) return(NULL)
    knownSegments <- data.frame(centromeres)
    colnames(knownSegments)[1] <- "chromosome"
    knownSegments$length <- knownSegments$end-knownSegments$start+1
    knownSegments$chromosome <- .strip.chr.name(knownSegments$chromosome,
        chr.hash)
    if (!is.null(breakpoints)) {
        knownSegments <- rbind(knownSegments[, 1:3], breakpoints)
    }    
    PSCBS::gapsToSegments(knownSegments)
}

.PSCBSoutput2DNAcopy <- function(seg, sampleid) {
    sx <- cbind(ID=sampleid, seg$output[!is.na(seg$output$tcnMean),])
    sx <- sx[,c("ID", "chromosome", "tcnStart", "tcnEnd", "tcnNbrOfLoci", 
        "tcnMean")]
    colnames(sx) <- c("ID", "chrom", "loc.start",  "loc.end", "num.mark", 
        "seg.mean")
    sx$seg.mean <- log2(sx$seg.mean/2)
    sx
}