diff --git a/Makefile b/Makefile
index 2b2fd39..f6425fe 100644
--- a/Makefile
+++ b/Makefile
@@ -22,6 +22,7 @@ rocks:
 	@${rocksDir}/bin/luarocks install --tree ${rocksDir} luacov
 	@${rocksDir}/bin/luarocks install --tree ${rocksDir} luacheck
 	@${rocksDir}/bin/luarocks install --tree ${rocksDir} busted
+	@${rocksDir}/bin/luarocks install --tree ${rocksDir} luasocket
 
 luacheck:
 	@${rocksDir}/bin/luacheck .
diff --git a/cherry/libs/shuffle-array.lua b/cherry/libs/shuffle-array.lua
new file mode 100644
index 0000000..789e1f6
--- /dev/null
+++ b/cherry/libs/shuffle-array.lua
@@ -0,0 +1,27 @@
+------------------------------------------------------------------
+
+local time = require 'cherry.libs.time'
+
+------------------------------------------------------------------
+-- https://stackoverflow.com/a/12646864
+-- Randomize array in-place using Durstenfeld shuffle algorithm
+------------------------------------------------------------------
+-- this function mutates the array
+------------------------------------------------------------------
+
+local function shuffleArray(array)
+  local seed = time.getTimeMs()
+  math.randomseed(seed)
+
+  for i = #array, 1, -1 do
+    local j = math.floor(math.random() * i) + 1
+    print(i, j)
+    local temp = array[i]
+    array[i] = array[j]
+    array[j] = temp
+  end
+end
+
+------------------------------------------------------------------
+
+return shuffleArray