Data commit

Task/Hash-join/Lua/hash-join-1.lua

@@ -0,0 +1,23 @@
+local function recA(age, name) return { Age=age, Name=name } end
+local tabA = { recA(27,"Jonah"), recA(18,"Alan"), recA(28,"Glory"), recA(18,"Popeye"), recA(28,"Alan") }
+
+local function recB(character, nemesis) return { Character=character, Nemesis=nemesis } end
+local tabB = { recB("Jonah","Whales"), recB("Jonah","Spiders"), recB("Alan","Ghosts"), recB("Alan","Zombies"), recB("Glory","Buffy") }
+
+local function hashjoin(taba, cola, tabb, colb)
+  local hash, join = {}, {}
+  for _,rowa in pairs(taba) do
+    if (not hash[rowa[cola]]) then hash[rowa[cola]] = {} end
+    table.insert(hash[rowa[cola]], rowa)
+  end
+  for _,rowb in pairs(tabb) do
+    for _,rowa in pairs(hash[rowb[colb]]) do
+      join[#join+1] = { A=rowa, B=rowb }
+    end
+  end
+  return join
+end
+
+for _,row in pairs(hashjoin(tabA, "Name", tabB, "Character")) do
+  print(row.A.Age, row.A.Name, row.B.Character, row.B.Nemesis)
+end

Task/Hash-join/Lua/hash-join-2.lua

@@ -0,0 +1,46 @@
+local hashlist = {
+  new = function(self,key)
+    return setmetatable({key=key, hash={}, list={}}, {__index=self})
+  end,
+  insert = function(self,row)
+    self.list[#self.list+1] = row
+    if not self.hash[row[self.key]] then self.hash[row[self.key]]={} end
+    table.insert(self.hash[row[self.key]], row)
+    return self
+  end,
+  join = function(self,tabb)
+    local result = {}
+    for _,rowb in pairs(tabb.list) do
+      if (self.hash[rowb[tabb.key]]) then
+        for _,rowa in pairs(self.hash[rowb[tabb.key]]) do
+          result[#result+1] = { A=rowa, B=rowb }
+        end
+      end
+    end
+    return result
+  end
+}
+
+local function recA(age, name) return { Age=age, Name=name } end
+tabA = hashlist:new("Name")
+  :insert(recA(27,"Jonah"))
+  :insert(recA(18,"Alan"))
+  :insert(recA(28,"Glory"))
+  :insert(recA(18,"Popeye"))
+  :insert(recA(28,"Alan"))
+
+local function recB(character, nemesis) return { Character=character, Nemesis=nemesis } end
+local tabB = hashlist:new("Character")
+  :insert(recB("Jonah","Whales"))
+  :insert(recB("Jonah","Spiders"))
+  :insert(recB("Alan","Ghosts"))
+  :insert(recB("Alan","Zombies"))
+  :insert(recB("Glory","Buffy"))
+
+for _,row in pairs(tabA:join(tabB)) do
+  print(row.A.Age, row.A.Name, row.B.Character, row.B.Nemesis)
+end
+print("or vice versa:")
+for _,row in pairs(tabB:join(tabA)) do
+  print(row.B.Age, row.B.Name, row.A.Character, row.A.Nemesis)
+end