UCLA FSPH R Files

dataTransformation

returnNonZeroRange.R

# by: Kevin Blansit, MS
# <kevin dot blansit at gmail dot com>

mtx <- rbind(
    c(0, 0, 0, 0, 1, 2, 3, 6, 0, 0, 0, 9),
    c(0, 3, 0, 0, 1, 2, 3, 6, 0, 0, 2, 3),
    c(0, 0, 3, 0, 1, 2, 3, 6, 0, 0, 2, 3),
    c(0, 0, 0, 0, 0, 0, 0, 6, 0, 0, 2, 3)
)


returnNonZeroRange <- function(mtx, bandwidth) {
    # mtx: the matrix input
    # bandwidth: the range of values to return
    
    findStart <- function(mtx) {
        # function to find the first non-zero of a matrix by row
        
        loc <- which(mtx != 0, arr.ind = TRUE)
        min_values <- aggregate(col ~ row, loc, min)$col
        if(length(min_values) != dim(mtx)[1]){
            stop(paste("The following matrix rows had all 0:",
                       paste0(which(rowSums(mtx == 0) == dim(mtx)[2]), collapse = ", ")))
        } else {
            return(min_values)
        }
    }
    if(bandwidth <= 0) {
        stop("bandwidth must be above 1")
    }
    # gives col index of first non-zero number
    start_vals <- findStart(mtx)
    
    m <- length(start_vals)
    
    add_mtx <- t(matrix(rep(0:(bandwidth-1), m), bandwidth))
    start_mtx <- matrix(rep(start_vals, bandwidth), m)
    col_mtx <- add_mtx + start_mtx
    
    if(max(col_mtx) > dim(mtx)[2]) {
        err_msg <- paste("bandwidth is larger than the supplied matrix;",
              "matrix cols: ",
              dim(mtx)[2],
              "; largest value requested: ",
              max(col_mtx),
              sep = "")
        stop(err_msg)
    }
    
    row_mtx <- matrix(rep(1:dim(mtx)[1], bandwidth), bandwidth)
    rslt_mtx <- cbind(row = c(row_mtx), col = c(col_mtx))
    
    # IGot99ProblemsButAnIndexAintOne
    return(matrix(mtx[rslt_mtx], ncol = bandwidth))
}

returnNonZeroRange(mtx, 5) # retunrs location matrix
returnNonZeroRange(mtx, 6) # this will not work since the last row doesn't have enough values to be valid

IGot99ProblemsButAnIndexAintOne