R/520-extractPCMBLOSUM.R

In BioMedR: Generating Various Molecular Representations for Chemicals, Proteins, DNAs/RNAs and Their Interactions

#' Generalized BLOSUM and PAM Matrix-Derived Descriptors
#' 
#' Generalized BLOSUM and PAM Matrix-Derived Descriptors
#' 
#' This function calculates the generalized BLOSUM matrix-derived descriptors.
#' For users' convenience, \code{BioMedR} provides the 
#' BLOSUM45, BLOSUM50, BLOSUM62, BLOSUM80, BLOSUM100, 
#' PAM30, PAM40, PAM70, PAM120, and PAM250 matrices 
#' for the 20 amino acids to select.
#' 
#' @param x A character vector, as the input protein sequence.
#' @param submat Substitution matrix for the 20 amino acids. Should be one of
#'        \code{AABLOSUM45}, \code{AABLOSUM50}, \code{AABLOSUM62}, 
#'        \code{AABLOSUM80}, \code{AABLOSUM100}, \code{AAPAM30}, 
#'        \code{AAPAM40}, \code{AAPAM70}, \code{AAPAM120}, \code{AAPAM250}.
#'        Default is \code{'AABLOSUM62'}.
#' @param k Integer. The number of selected scales (i.e. the first 
#'        \code{k} scales) derived by the substitution matrix.
#'        This could be selected according to the printed relative 
#'        importance values.
#' @param lag The lag parameter. Must be less than the amino acids.
#' @param scale Logical. Should we auto-scale the substitution matrix 
#'        (\code{submat}) before doing eigen decomposition? Default is 
#'        \code{TRUE}.
#' @param silent Logical. Whether we print the relative importance of 
#'        each scales (diagnal value of the eigen decomposition result matrix B) 
#'        or not.
#'        Default is \code{TRUE}.
#' @return  A length \code{lag * p^2} named vector, 
#'         \code{p} is the number of scales selected.
#' 
#' @keywords extract BLOSUM extrPCMBLOSUM PCM
#'
#' @aliases extrPCMBLOSUM
#' 
#' @author Min-feng Zhu <\email{wind2zhu@@163.com}>, 
#'         Nan Xiao <\url{http://r2s.name}>
#' 
#' @export extrPCMBLOSUM
#' 
#' @references
#' Georgiev, A. G. (2009). 
#' Interpretable numerical descriptors of amino acid space. 
#' Journal of Computational Biology, 16(5), 703--723.
#' 
#' @examples
#' x = readFASTA(system.file('protseq/P00750.fasta', package = 'BioMedR'))[[1]]
#' blosum = extrPCMBLOSUM(x, submat = 'AABLOSUM62', k = 5, lag = 7, scale = TRUE, silent = FALSE)
#' 

extrPCMBLOSUM = function (x, submat = 'AABLOSUM62', k, lag, 
                             scale = TRUE, silent = TRUE) {

    if (checkProt(x) == FALSE) stop('x has unrecognized amino acid type')

    k = min(k, 20)

    submat = get(submat)
    if (scale) submat = scale(submat)

    eig = eigen(submat)
    A = eig$vectors
    B = eig$values
    rownames(A) = rownames(submat)
    # the equation: submat == A %*% diag(B) %*% t(A)

    accmat = matrix(0, k, nchar(x))
    x.split = strsplit(x, '')[[1]]

    for (i in 1:nchar(x)) {
        accmat[, i] = A[x.split[i], 1:k]
    }

    result = acc(accmat, lag)

    if (!silent) {
        cat('Relative importance of all the possible 20 scales:\n')
        print(B)
    }

    return(result)

}