如何根据另一个字符串表定义的顺序对字符串表进行排序（Lua）

Posted 2023-03-28

【中文标题】如何根据另一个字符串表定义的顺序对字符串表进行排序（Lua）

【英文标题】：How to Sort a table of strings according to the order defined by another table of strings (Lua)

【发布时间】：2021-12-20 20:05:48

【问题描述】：

我有 2 个 lua 表：

OrderTbl = 'Hello', 'Question', 'Answer', 'Bye'
UnsortedTbl = 'Question', 'Bye, 'Bye', 'Question', 'Hello', 'Something'

如何按照 OrderTbl 给出的顺序对 UnsortedTbl 进行排序？ （OrderTbl中没有找到的字段放在结果表的末尾，未排序）

我已经从 Java 翻译了一个代码示例，它可以与 numbers 一起使用。这里是：

function first(arr, low, high, x, n)
    if high >= low then
    
        -- (low + high)/2
        local mid = low + math.floor((high - low) / 2)
        
        if (mid == 1 or x > arr[mid - 1]) and arr[mid] == x then
            return mid
        end
        if x > arr[mid] then return first(arr, (mid + 1), high, x, n) end
        return first(arr, low, (mid - 1), x, n)
    end
    return nil
end

-- Sort A1 according to the order
-- defined by A2
function sortAccording(A1, A2)
    local m=#A1
    local n=#A2

    -- The temp array is used to store a copy
    -- of A1 and visited is used to mark the
    -- visited elements in temp.
    local temp = 
    local visited = 

    for i = 1, m do
        temp[i] = A1[i]
        visited[i] = 0
    end

    -- Sort elements in temp
    table.sort(temp)

    -- for index of output which is sorted A1
    local ind = 0

    -- Consider all elements of A2, find them
    -- in temp and copy to A1 in order.
    for i = 1, n do
        -- Find index of the first occurrence
        -- of A2[i] in temp
        local f = first(temp, 1, m, A2[i], m+1)
        -- If not present, no need to proceed
        if not f then
            -- continue
        else
            -- Copy all occurrences of A2[i] to A1
            j = f
            while j < m and temp[j] == A2[i] do
                A1[ind] = temp[j]
                ind = ind + 1
                visited[j] = 1
                j = j + 1
            end
        end
    end
    -- Now copy all items of temp which are
    -- not present in A2
    for i = 1, m do
        if visited[i] == 0 then
            ind = ind + 1
            A1[ind] = temp[i]
        end
    end

end

function printArray(arr)
    for i = 1, #arr do 
        print(arr[i] .. " ") 
    end
end

-- Driver program to test above function.
local A1 = 2, 1, 2, 5, 7, 1, 9, 3, 6, 8, 8
local A2 = 2, 1, 4, 3, 6, 5, 8, 7

sortAccording(A1, A2)
printArray(A1)

我不太明白如何使它与 strings 一起工作。你能帮帮我吗？

【问题讨论】：

如果您阅读手册，您会看到table.sort 带有一个可选的第二个参数。你知道它有什么用吗？

是的，我已经在学习了:)

【参考方案1】：

您可以使用接受自定义比较器的table.sort 形式：

local OrderTbl = 'Hello', 'Question', 'Answer', 'Bye'
local UnsortedTbl = 'Question', 'Bye', 'Bye', 'Question', 'Hello', 'Something', 'Else'

-- convert the order to hash that can be easily queried
for idx, val in ipairs(OrderTbl) do OrderTbl[val] = idx end

local maxIdx = #OrderTbl + 1 -- this will mark "missing" elements
-- pass a custom comparator that will check OrderTbl
table.sort(UnsortedTbl, function(a, b)
    local pa = OrderTbl[a] or maxIdx -- desired index of a
    local pb = OrderTbl[b] or maxIdx -- desired index of b
    if pa == pb then return a < b end -- sort by name
    return pa < pb -- sort by index
  end)