skewness index added

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: tourr
 Title: Tour Methods for Multivariate Data Visualisation
-Version: 1.2.1
+Version: 1.2.2
 Authors@R: c(
  person("Hadley", "Wickham", email = "h.wickham@gmail.com", role = c("aut", "ctb"), comment = c(ORCID = "0000-0003-4757-117X")),
  person("Dianne", "Cook", email = "dicook@monash.edu", role = c("aut", "cre"), comment = c(ORCID = "0000-0002-3813-7155")),

NAMESPACE

@@ -108,6 +108,7 @@ export(search_better_random)
 export(search_geodesic)
 export(search_polish)
 export(search_posse)
+export(skewness)
 export(slice_index)
 export(sphere_data)
 export(splines2d)

NEWS.md

@@ -1,3 +1,7 @@
+# tourr 1.2.2
+
+* New skewness index, as defined in original Cook, Buja, Cabrera paper
+
 # tourr 1.2.1
 
 * anomaly tour is initialised with a random basis

R/interesting-indices.r

@@ -128,6 +128,25 @@ cmass <- function() {
  }
 }
 
+#' Skewness index.
+#'
+#' Calculates the skewness index. See Cook, Buja and Cabrera (1993)
+#' Projection pursuit indexes based on orthonormal function expansions
+#' for equations.
+#'
+#' @keywords hplot
+#' @export
+skewness <- function() {
+ function(mat) {
+ n <- nrow(mat)
+ d <- ncol(mat)
+
+ idx <- mean(rowSums(mat * exp(-0.5 * mat^2)))
+
+ idx
+ }
+}
+
 #' LDA projection pursuit index.
 #'
 #' Calculate the LDA projection pursuit index. See Cook and Swayne (2007)