RによるMATTRの実装 https://github.com/rongmu/mattr

mattr.R

# An alternative implementation of the MATTR algorithm in R
# author: Shaoyun YU <eric.rongmu@gmail.com>
# ref: Covington & Mcfall (2010) Cutting the Gordian Knot: The Moving-Average Type-Token Ratio
# usage: mattr(vector_of_tokens, window_size)

window_types <- function(i_start, win_size, data) {
  i_end <- i_start + win_size - 1

  win <- data[i_start:i_end]

  length(unique(win))
}


mattr <- function(x, win_size, full.pass = FALSE) {
  if (full.pass) {
    x <- c(x, x[1:(win_size - 1)])
  }

  n_win <- length(x) - win_size + 1

  types <- vapply(seq_len(n_win), window_types, integer(1),
                  win_size = win_size, data = x)

  mean(types) / win_size
}