使用所选键循环访问表

Question

下表和 for 循环是我们通常访问 lua 中所有键、值对的方式

local t = {a1 =11, a2=22, c=3, d=4}
for k, v in pairs(t) do
print(k,v)
end
-- Output: k = a1, a2, c, d & v = 11, 22, 3, 4 respectively
a1 11  
a2 22
c  3
d  4

如果我只想迭代此表的子集，其中循环仅迭代某些键，如下所示

k = a1,a2 

由于我打算在t中添加更多表

local t = {
{a1 = 11, a2 = 22, c = 3, d = 4},
{a1 = 12, a2 = 23, c = 2, d = 4},
{a1 = 13, a2 = 24, c = 1, d = 4},
{a1 = 14, a2 = 25, c = 0, d = 4},
{a1 = 15, a2 = 26, c = 0, d = 4}
}

我想使用类似的东西

for k = {a1, a2} in pairs (t) do
-- something
end

除了在循环中添加 if 条件之外，有没有办法做到这一点，因为这将遍历所有 k，v 对并且不需要

for k,v in pairs (t) do
if (k == a1 or k == a2) then
-- something

Answer 1

你可以这样做

local t = {
{a1 = 11, a2 = 22, c = 3, d = 4},
{a1 = 12, a2 = 23, c = 2, d = 4},
{a1 = 13, a2 = 24, c = 1, d = 4},
{a1 = 14, a2 = 25, c = 0, d = 4},
{a1 = 15, a2 = 26, c = 0, d = 4}
}
local keys_to_iterate = {"a1", "a2"}
for index = 1, #t do
for k = 1, #keys_to_iterate do
if t[index][keys_to_iterate[k]] then
print(keys_to_iterate[k] , t[index][keys_to_iterate[k]])
end
end
end

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