bnp

commit 22c63244aa68fcf0cc8d577dc248ca9a87d82aa5
parent ca36a3f2f866e4876afe3dbe029776a2edb9c6f2
Author: Jared Tobin <jared@jtobin.ca>
Date:   Wed, 17 Feb 2016 17:22:31 +1300

IBP skeleton.

Diffstat:
A
indian-buffet-process/src/ibp.r
 | 
38
++++++++++++++++++++++++++++++++++++++

1 file changed, 38 insertions(+), 0 deletions(-)
diff --git a/indian-buffet-process/src/ibp.r b/indian-buffet-process/src/ibp.r
@@ -0,0 +1,38 @@
+# FIXME handle sampled zero values
+
+ibp = function(n, a) {
+  dishes = rpois(1, a)
+  diners = data.frame(dish = seq(dishes), diners = rep(1, dishes))
+  buffet = list(buffet = diners, choices = list(seq(dishes)))
+
+  for (j in seq(n - 1)) {
+      buffet = arrival(buffet, a)
+    }
+  buffet
+  }
+
+arrival = function(b, a) {
+
+  config  = b$buffet
+  choices = b$choices
+
+  j          = length(choices) + 1
+  n          = nrow(config)
+  probs      = sapply(config$diners, function(n) { n / j })
+  selection  = rbinom(n, 1, prob = probs) == 1
+
+  existing_diners = config[selection, 'diners']
+  new_diners = with(config, replace(diners, selection, diners[selection] + 1))
+
+  existing_dishes = data.frame(dish = config$dish, diners = new_diners)
+  num_new_dishes  = rpois(1, a / j )
+  new_dishes = data.frame(
+      dish   = (n + 1):(n + num_new_dishes)
+    , diners = rep(1, num_new_dishes)
+    )
+
+  list(
+      buffet  = rbind(existing_dishes, new_dishes)
+    , choices = list(choices, rep(TRUE, num_new_dishes)) # FIXME
+    )
+  }