R/demultiplexFastq.R

In UMI4Cats: UMI4Cats: Processing, analysis and visualization of UMI-4C chromatin contact data

#' Demultiplex FASTQ files using fastq-multx
#'
#' Demultiplex FASTQ files containng different bait information
#' @param barcodes Dataframe with "name of sample" and "barcode" for every
#' sample to demultiplex.
#' @param fastq Fastq to demultiplex containing mate 1s. Different pairs should
#' be named as "_R1" or "_R2". Allowed formats: _R1.fastq.gz, _R1.fq.gz, _R1.fastq
#' or _R1.fq.
#' @param numb_reads Number of lines from the FastQ file to load in each loop.
#' If having memory size problems, change it to a smaller number. Default=10e10.
#' @param out_path Path where to save the demultiplex output. Defaults to a path
#'  named \code{raw_fastq} in your working directory.
#' @return Paired-end FastQ files demultiplexed in a compressed format. A log file with the statistics
#' is also generated in \code{out_path} named \code{barcode}_umi4cats_demultiplexFastq_stats.txt.
#' @examples
#' \dontrun{
#' path <- downloadUMI4CexampleData(use_sample = TRUE)
#' fastq <- file.path(path, "CIITA", "fastq", "sub_ctrl_hi19_CIITA_R1.fastq.gz")
#' barcodes <- data.frame(
#'     sample = c("CIITA"),
#'     barcode = c("GGACAAGCTCCCTGCAACTCA")
#' )
#'
#' demultiplexFastq(
#'     barcodes = barcodes,
#'     fastq = fastq,
#'     out_path = path
#' )
#' }
#'
#' @export
demultiplexFastq <- function(barcodes,
    fastq,
    out_path = "raw_fastq",
    numb_reads = 10e10) {
    fq_R1 <- fastq
    fq_R2 <- gsub("_R1.", "_R2.", fq_R1)

    extension_fastq <- utils::tail(unlist(strsplit(fq_R1, "_")), n = 1)

    if (!extension_fastq %in% c("R1.fastq.gz", "R1.fq.gz", "R1.fastq", "R1.fq")) {
        stop(paste("FASTQ file should have one of the following extensions:
               _R1.fastq.gz, _R1.fq.gz, _R1.fastq or _R1.fq"))
    }

    if (length(fq_R2) == 0) stop(paste("Files should be paired-end type"))

    if (!is(barcodes, "data.frame")) stop(paste("Barcodes should be a Dataframewith name of sample and barcode for every sample to demultiplex"))

    message(paste(
        "Starting demultiplex using:\n",
        "> Barcodes:\n", paste(utils::capture.output(print(barcodes)),
            collapse = "\n"
        ), "\n\n",
        "> File R1:", fq_R1, "\n",
        "> File R2:", fq_R2, "\n",
        "> Output path:", out_path
    ))



    # Initialize global variables
    total_reads <- 0
    specific_reads <- 0


    for (i in seq_len(nrow(barcodes))) {
        stream1 <- ShortRead::FastqStreamer(fq_R1)
        stream2 <- ShortRead::FastqStreamer(fq_R2)

        # generate barcode
        barcode <- barcodes$barcode[i]

        repeat {
            reads_fqR1 <- ShortRead::yield(stream1, n = numb_reads)
            reads_fqR2 <- ShortRead::yield(stream2, n = numb_reads)

            if (length(reads_fqR1) == 0) break
            if (length(reads_fqR1) != length(reads_fqR2)) stop("Different number of reads in R1 vs R2")

            total_reads <- total_reads + length(reads_fqR1) # Save total reads

            # for cases when the bait is to far from restriction enzyme
            if (nchar(as.character(barcode)) > unique(ShortRead::width(reads_fqR1))) {
                barcode <- substr(barcode, 1, unique(width(reads_fqR1)))
            }

            # filter reads that not present barcode
            barcode_reads_fqR1 <- reads_fqR1[grepl(barcode, ShortRead::sread(reads_fqR1))]
            barcode_reads_fqR2 <- reads_fqR2[grepl(barcode, ShortRead::sread(reads_fqR1))]

            specific_reads <- specific_reads + length(barcode_reads_fqR1) # Save specific reads

            # write output fastq files
            output_fastq <- file.path(out_path, barcodes$sample[i])

            ShortRead::writeFastq(barcode_reads_fqR1,
                paste0(output_fastq, "_R1.fq.gz"),
                mode = "a"
            )

            ShortRead::writeFastq(barcode_reads_fqR2,
                paste0(output_fastq, "_R2.fq.gz"),
                mode = "a"
            )
        }

        # Construct stats data.frame
        stats <- data.frame(
            sample_id = barcodes$sample[i],
            total_reads = total_reads,
            specific_reads = specific_reads,
            stringsAsFactors = FALSE
        )

        # create stats file and save
        stats <- do.call(rbind, stats)
        utils::write.table(stats,
            file = file.path(
                out_path,
                paste0(
                    barcodes$sample[i],
                    "_umi4cats_demultiplexFastq_stats.txt"
                )
            ),
            row.names = FALSE,
            sep = "\t",
            quote = FALSE
        )

        message("Finished demultiplex sample ", barcodes$sample[i])
    }

    on.exit(close(stream1))
    on.exit(close(stream2), add = TRUE)
}