From 2d7fa98155bfa274ac254ba015bea27b7aa5a751 Mon Sep 17 00:00:00 2001
From: rxi <rxi@users.noreply.github.com>
Date: Wed, 12 Mar 2014 13:12:45 +0000
Subject: [PATCH] Added lume.weightedchoice()

---
 README.md | 11 +++++++++++
 lume.lua  | 15 +++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/README.md b/README.md
index 42141a6..c457cc1 100644
--- a/README.md
+++ b/README.md
@@ -64,6 +64,17 @@ raised.
 lume.randomchoice({true, false}) -- Returns either true or false
 ```
 
+### lume.weightedchoice(t)
+Takes the argument table `t` where the keys are the possible choices and the
+values are the choice's weight. A weight should be 0 or above, the larger the
+weight value the higher the probability of that choice being picked. If the
+table is empty or all the weights are 0 or a weight is below zero an error is
+raised.
+```lua
+lume.weightedchoice({ ["cat"] = 10, ["dog"] = 5, ["frog"] = 0 })
+-- Returns either "cat" or "dog" with "cat" being twice as likely to be chosen.
+```
+
 ### lume.shuffle(t)
 Shuffles the values of array `t` in place, returns the array.
 
diff --git a/lume.lua b/lume.lua
index 2de5867..b06980d 100644
--- a/lume.lua
+++ b/lume.lua
@@ -67,6 +67,21 @@ function lume.randomchoice(t)
 end
 
 
+function lume.weightedchoice(t)
+  local sum = 0
+  for k, v in pairs(t) do
+    assert(v >= 0, "weight value less than zero")
+    sum = sum + v
+  end
+  assert(sum ~= 0, "all weights are zero")
+  local rnd = lume.random(sum)
+  for k, v in pairs(t) do
+    if rnd < v then return k end
+    rnd = rnd - v
+  end
+end
+
+
 function lume.shuffle(t)
   for i = 1, #t do
     local r = math.random(#t)