

Skye(MASS)                                   R Documentation

_A_F_M _C_o_m_p_o_s_i_t_i_o_n_s _o_f _A_p_h_y_r_i_c _S_k_y_e _L_a_v_a_s

_D_e_s_c_r_i_p_t_i_o_n_:

     The `Skye' data frame has 23 rows and 3 columns.

_A_r_g_u_m_e_n_t_s_:

       A: Percentage of sodium and potassium oxides

       F: Percentage of iron oxide

       M: Percentage of magnesium oxide

_F_o_r_m_a_t_:

     This data frame contains the following columns:

_S_o_u_r_c_e_:

     J. Aitchison (1986) The Statistical Analysis of Compo-
     sitional Data.  Chapman and Hall, p.360.

     R.N. Thompson, J. Esson and A.C. Duncan (1972) Major
     element chemical variation in the Eocene lavas of the
     Isle of Skye.  J. Petrology 13, 219-253.

_E_x_a_m_p_l_e_s_:

     # ternary() is from the on-line answers.
     ternary <- function(X, pch = par("pch"), lcex = 1,
                         add = FALSE, ord = 1:3, ...)
     {
       X <- as.matrix(X)
       if(any(X) < 0) stop("X must be non-negative")
       s <- drop(X %*% rep(1, ncol(X)))
       if(any(s<=0)) stop("each row of X must have a positive sum")
       if(max(abs(s-1)) > 1e-6) {
         warning("row(s) of X will be rescaled")
         X <- X / s
       }
       X <- X[, ord]
       s3 <- sqrt(1/3)
       if(!add)
       {
         oldpty <- par("pty")
         on.exit(par(pty=oldpty))
         par(pty="s")
         plot(c(-s3, s3), c(0.5-s3, 0.5+s3), type="n", axes=FALSE,
              xlab="", ylab="")
         polygon(c(0, -s3, s3), c(1, 0, 0), density=0)
         lab <- NULL
         if(!is.null(dn <- dimnames(X))) lab <- dn[[2]]
         if(length(lab) < 3) lab <- as.character(1:3)
         eps <- 0.05 * lcex
         text(c(0, s3+eps*0.7, -s3-eps*0.7),
              c(1+eps, -0.1*eps, -0.1*eps), lab, cex=lcex)
       }
       points((X[,2] - X[,3])*s3, X[,1], ...)
     }

     data(Skye)
     ternary(Skye/100, ord=c(1,3,2))

