R/filter_mscore_freqobs.R

In SWATH2stats: Transform and Filter SWATH Data for Statistical Packages

#' Filter OpenSWATH output table according to mscore.
#'
#' This function filters the SWATH data according to the m_score value, as well
#' as to the number of occurence in the data.
#'
#' @param data  A data frame containing SWATH data.
#' @param mscore  Value that defines the mscore threshold according to which the
#'   data will be filtered.
#' @param percentage  Percentage in which replicas the transition has to reach
#'   the mscore threshold.
#' @param rm.decoy  Option to remove the decoys during filtering.
#' @param mscore.col Defines the column from which to retrieve the m_score. 
#'    If you use JPP (Rosenberger, Bludau et al. 2017) this can be used to 
#'    select between Protein and transition_group m_score.
#' @return Returns a data frame with the filtered data.
#' @author Peter Blattmann
#' @examples
#'  data("OpenSWATH_data", package="SWATH2stats")
#'  data("Study_design", package="SWATH2stats")
#'  data <- sample_annotation(OpenSWATH_data, Study_design)
#'  data.filtered <- filter_mscore(data, 0.01)
#'  data.filtered <- filter_mscore_freqobs(data, 0.01, 0.8)
#'  data.filtered <- filter_mscore_condition(data, 0.01, 3)
#' @export

filter_mscore_freqobs <- function(data, 
                                  mscore, 
                                  percentage = NULL, 
                                  rm.decoy = TRUE,
                                  mscore.col = "m_score") {
    
    mscore.col <- JPP_update(data, mscore.col)

    data$Peptide_Charge <- paste(data$FullPeptideName, data$Charge)
    if (sum(colnames(data) == "decoy") == 1 & isTRUE(rm.decoy)) {
        # data <- subset(data, decoy == 0)
        data <- data[data$decoy == 0, ]
    }

    # data.filtered <- subset(data, m_score <= mscore)
    data.filtered <- data[data[, mscore.col] <= mscore, ]
    data.filtered <- data.table::data.table(data.filtered)

    data.filtered <- data.filtered[, c("Peptide_Charge", "aggr_Peak_Area"), with = FALSE]
    data.table::setkeyv(data.filtered, cols = "Peptide_Charge")
    .N <- NULL
    data.n <- data.filtered[, .N, by = "Peptide_Charge"]

    if (is.null(percentage)) {
        percentage <- 0
    }

    threshold <- nlevels(factor(data$filename)) * percentage
    message("Treshold, peptides need to have been quantified in more conditions than: ",
        threshold)

    peptides.filtered <- data.n[data.n$N >= threshold]
    peptides.filtered <- data.frame(Peptides_Charge = peptides.filtered$Peptide_Charge)

    message("Fraction of peptides selected: ",
            signif(length(unique(peptides.filtered$Peptides_Charge)) /
                   length(unique(data$Peptide_Charge)),
                   digits = 2))

    data.filtered <- merge(data, peptides.filtered,
                           by.x = "Peptide_Charge", by.y = "Peptides_Charge")
    message("Dimension difference: ", paste(dim(data) - dim(data.filtered), collapse = ", "))
    return(data.filtered)
}