R/describe.R

In Bolstad2: Bolstad Functions

#' Give simple descriptive statistics for a matrix or a data frame
#' 
#' This function is designed to emulate the Minitab function DESCRIBE. It gives
#' simple descriptive statistics for a data frame
#' 
#' 
#' @param x A matrix or data.frame with numeric entries. Different variables
#' are represented by columns.
#' @param varNames A vector of variable names for each of the columns
#' @return A data.frame containing the following elements: \item{N}{The number
#' of observations for each variable} \item{mean}{The sample mean for each
#' variable} \item{stdev}{The sample standard deviation} \item{sterr}{The
#' standard error of the mean} \item{min}{The minimum} \item{q1}{The lower
#' quartile} \item{med}{The median} \item{q3}{The upper quartile}
#' \item{max}{The maximum}
#' @examples
#' 
#' data(poissonTest.df)
#' describe(poissonTest.df)
#' 
#' @export describe
describe = function(x, varNames = NULL) {
    ## Mimics Minitab's desc function

    nameX = deparse(substitute(x))

    if (is.matrix(x)) {
        x = data.frame(x)
        if (is.null(varNames))
            varNames = paste(nameX, 0:(ncol(x) - 1), sep = "")
        names(x) = varNames
    }

    nx = sapply(x, length)
    mx = sapply(x, mean)
    sx = sapply(x, sd)
    SEx = sapply(x, sd)/sqrt(nx)
    minx = sapply(x, min)
    maxx = sapply(x, max)
    q1x = sapply(x, quantile, prob = 0.25)
    medx = sapply(x, median)
    q3x = sapply(x, quantile, prob = 0.75)

    stats.df = data.frame(N = nx, mean = mx, stdev = sx, sterr = SEx, min = minx, q1 = q1x, med = medx,
        q3 = q3x, max = maxx)

    nVars = ncol(x)

    print(stats.df)

    invisible(stats.df)
}