added r data module

R/hhi.R

@@ -0,0 +1,17 @@
+# Community Data Science Collective R Utilities
+#
+# Copyright (c) 2010-2016 Benjamin Mako Hill and Aaron Shaw 
+# mako@atdot.cc, aaronshaw@northwestern.edu
+
+## functions to create normal and non-normalized herfenidahl indexes
+hhi <- function (x) {
+  x <- x / sum(x)
+  sum(x**2)
+}
+
+hhi.norm <- function (x) {
+  n <- length(x)
+  h <- hhi(x)
+  (h - 1/n)/(1-1/n)
+}
+