R/utils.R

In zFactor: Calculate the Compressibility Factor 'z' for Hydrocarbon Gases

# A dataframe with information about any of the compressibility correlation available
z_correlations <- data.frame(
    short = c("BB", "HY", "DAK", "DPR", "SH", "N10", "PP"),
    long = c("Beggs-Brill", "Hall-Yarborough", "Dranchuk-AbuKassem",
             "Dranchuk-Purvis-Robinson", "Shell", "Ann10", "Papp"),
    function_name = c("z.BeggsBrill", "z.HallYarborough", "z.DranchukAbuKassem",
                      "z.DranchukPurvisRobinson", "z.Shell", "z.Ann10", "z.Papp"),
    stringsAsFactors = FALSE
)


#' Get correlation information
#'
#' Get information about the correlation specifying for short name, long name or
#' the name of the function.
#'
#' @param how short: abbreviations; long: description; function: the name of the
#' correlation function
#' @export
#' @rdname get_z_correlations
#' @examples
#' # get the short name for the correlation
#' get_z_correlations(how = "short")
#'
#' # get the description for the correlation
#' get_z_correlations(how = "long")
#'
#' # get the name of the function assgined to the correlation
#' get_z_correlations(how = "function")
get_z_correlations <- function(how = "short") {
    # get correlation information. short: abbreviations; long: description
    #     function: the name of the correlation function
    if (how == "short")
        return(z_correlations[["short"]])
    if (how == "long")
        return(z_correlations[["long"]])
    if (how == "function")
        return(z_correlations[["function_name"]])
    else stop("wrong keyword")
}



#' split a long string to create a vector for testing
#'
#' @param str a contnuous long string to split as a vector
#' @export
#' @examples
#' convertStringToVector("1.05 1.10 1.20")
#' # result: "c(1.05, 1.1, 1.2)"
#' # now, you can paste the vector in your test
convertStringToVector <- function(str) {
    vs <- unlist(strsplit(str, " "))
    vs <- vs[lapply(vs, nchar) > 0]
    # prevent warning message:  introducing NAs by coercion
    # https://stackoverflow.com/a/14985152/5270873
    vn <- suppressWarnings(as.numeric(vs))
    if(all(is.na(vn))) vt <- paste(trimws(vs), collapse = ", ")
    else vt <- paste(vn, collapse = ", ")
    paste0('c(', vt, ')')
}


matrixToDataframe <- function(mat) {
    # convert a Ppr/Tpr matrix do a dataframe
    mat <- cbind(as.double(rownames(mat)), mat)  # new column for Tpr
    rownames(mat) <- NULL           # reset row names
    df <- as.data.frame(mat)        # dataframe
    names(df)[1] <- "Tpr"
    df
}


matrixWithCorrelation <- function(ppr_vector, tpr_vector, corr.Function) {
    # create a matrix using a z-factor correlation function and sapply
    co <- sapply(ppr_vector, function(x)
        sapply(tpr_vector, function(y) corr.Function(pres.pr = x, temp.pr = y)))

    if (length(ppr_vector) > 1 || length(tpr_vector) > 1) {
        co <- matrix(co, nrow = length(tpr_vector), ncol = length(ppr_vector))
        rownames(co) <- tpr_vector
        colnames(co) <- ppr_vector
    }
    co
}


combineCorrWithSK <- function(sk_df, co_df) {
    # combine correlation tidy DF with Standing-Katz tidy DF
    sk_cols <- ncol(sk_df)
    co_cols <- ncol(co_df)
    sk_tidy <- tidyr::gather(sk_df, "ppr", "z.chart", 2:sk_cols)
    co_tidy <- tidyr::gather(co_df, "ppr", "z.calcs", 2:co_cols)

    sk_co_tidy <- cbind(sk_tidy, z.calc = co_tidy$z.calcs)
    sk_co_tidy$dif <- sk_co_tidy$z.chart  - sk_co_tidy$z.calc
    colnames(sk_co_tidy)[1:2] <- c("Tpr", "Ppr")
    sk_co_tidy$Tpr <- as.character(sk_co_tidy$Tpr)
    sk_co_tidy$Ppr <- as.numeric(sk_co_tidy$Ppr)
    sk_co_tidy
}


#' Create a tidy table from Ppr and Tpr vectors
#'
#' @param ppr_vector a pseudo-reduced pressure vector
#' @param tpr_vector a pseudo-reduced temperature vector
#' @param correlation a z-factor correlation
#' @export
#' @examples
#' ppr <- c(0.5, 1.5, 2.5, 3.5)
#' tpr <- c(1.05, 1.1, 1.2)
#' createTidyFromMatrix(ppr, tpr, correlation = "DAK")
#' createTidyFromMatrix(ppr, tpr, correlation = "BB")
createTidyFromMatrix <- function(ppr_vector, tpr_vector, correlation) {
    msg <- "You have to provide a z-factor correlation: "
    msg_missing <- paste(msg, paste(get_z_correlations(), collapse = " "))
    if (missing(correlation)) stop(msg_missing)

    if (!isValid_correlation(correlation)) stop("Not a valid correlation.")

    zFunction <- get(z_correlations[which(z_correlations["short"] == correlation),
                                    "function_name"])

    sk_matrix <- getStandingKatzMatrix(ppr_vector, tpr_vector,
                                       pprRange = "lp")
    co_matrix <- matrixWithCorrelation(ppr_vector, tpr_vector,
                                       corr.Function = zFunction)

    sk_df <- matrixToDataframe(sk_matrix)
    co_df <- matrixToDataframe(co_matrix)

    sk_co_tidy <- combineCorrWithSK(sk_df, co_df)
    sk_co_tidy
}



#' Check if supplied correlation (three letter) is valid
#'
#' @param correlation a z-factor correlation
#' @export
isValid_correlation <- function(correlation) {
    # check if supplied correlation is valid
    valid_choices <- z_correlations[["short"]]      # get vector of correlations
    ifelse(correlation %in% valid_choices, TRUE, FALSE)
}