映射可变参数函数 lua

Question

我希望能够映射带有多个参数的函数，例如

    function(a, b) return a+b end

到 table 这样我就可以写像

    answer = varmap(function(a, b) return a+b end, {1, 7, 3}, {5, 4, 8}

但我不喜欢 table 使用 lua 可变参数，wikibooks 上的 code samples 使用 table.getn，当你用 # 替换它们时不起作用并且 returns“attempt to preform arithmatic on local 'a' (a nil value)”

Answer 1

也许您正在寻找这样的东西：

function varmapn(func, ...)
   local args, result = { ... }, {}
   for arg_i = 1, #(args[1]) do
      local call_args = {}
      for arg_list = 1, #args do
         table.insert(call_args, args[arg_list][arg_i])
      end
      table.insert(result, func(table.unpack(call_args)))
   end
   return result
end

交互示例：

> answer = varmapn(function (a, b) return a+b end, {1, 7, 3}, {5, 4, 8})
> print(answer)
table: 0x970eb0
> for i = 1, 3 do print(answer[i]) end
6
11
11

或者，这里稍微复杂一点的功能比较通用。对于参数列表，它采用数组，或者采用具有任意键的表：

function mapn(func, ...)
   local args, call_args = { ... }, {}
   local result = {}

   for k in pairs(args[1]) do
      call_args[k] = {}
   end   

   for arg_list, v in pairs(args) do
      for k in pairs(args[1]) do      
         table.insert(call_args[k], v[k])
      end
   end
   for k, v in pairs(call_args) do
      result[k] = func(table.unpack(v))
   end
   return result
end

交互示例：

> answer = mapn(function (a, b) return a+b end, {x=1, y=7, z=3}, {x=5, y=4, z=8})
> for k,v in pairs(answer) do print(k .. " = " .. v) end
z = 11
y = 11
x = 6
> answer = mapn(function (a, b) return a+b end, {1, 7, 3}, {5, 4, 8})
> for i = 1, 3 do print(answer[i]) end
6
11
11

Answer 2

local function imap(func, ...)  -- imap(func, src_table_1, src_table_2, ...)
   local result = {}
   local src_tables_arr = {...}
   if #src_tables_arr == 1 then
      for k, v in ipairs(src_tables_arr[1]) do
         result[k] = func(v)
      end
   else
      for k = 1, #src_tables_arr[1] do
         result[k] = func(
                             (table.unpack or unpack)
                             (
                                imap(
                                   function(src_t) return src_t[k] end,
                                   src_tables_arr
                                )
                             )
                         )
      end
   end
   return result
end
table.imap = imap

用法：

local arr = table.imap(function (a, b) return a+b end, {1, 7, 3}, {5, 4, 8})

Answer 3

还有一种可能：

local unpack = table.unpack or unpack

--------------------------------------------------------------------------------
-- Python-like zip() iterator
--------------------------------------------------------------------------------

function zip(...)
  local arrays, ans = {...}, {}
  local index = 0
  return
    function()
      index = index + 1
      for i,t in ipairs(arrays) do
        if type(t) == 'function' then ans[i] = t() else ans[i] = t[index] end
        if ans[i] == nil then return end
      end
      return ans
    end
end

--------------------------------------------------------------------------------

function map(f,...)
  assert(type(f) == 'function','Function expected for 1st arg')
  local t = {...}
  return coroutine.wrap(
         function()
           for t in zip(unpack(t)) do
             coroutine.yield(f(unpack(t)))
           end
         end)
end

--------------------------------------------------------------------------------
-- Example use

for item in map(function(a, b) return a+b end, {1, 7, 3}, {5, 4, 8}) do
  print(item)
end

print()

for item in map(function(a) return a*2 end, {1, 7, 3}) do
  print(item)
end

映射可变参数函数 lua

map varargs function lua

lua

functional-programming

variadic-functions

map-function