联合迭代器的地图？ [英] Union iterator for maps?

问题描述

前言像 std :: map 这样的关联C ++容器有点像微数据库，只有一个键列。 Boost的 bimap 将这个提升为一个两列的表，在这两列中都有查找，但这就是类比 - 没有polymap概括的想法。 ]

[Preface: The associative C++ containers like std::map are a bit like micro-databases with just one key column. Boost's bimap elevates this to a two-column table with lookup in both columns, but that that's as far as the analogy goes -- there's no "polymap" that generalizes the idea.]

无论如何，我想继续把地图视为数据库，现在我想知道是否有一个迭代器（或其他解决方案）允许我做一个UNION的几个成分映射。也就是说，所有的映射都具有相同的类型（或者值类型和比较器，至少），我想要一个迭代器，将整个集合作为一个大的多重映射（重复键是OK），让我在正确的联合

In any event, I want to keep thinking of maps as databases, and I now wonder if there is an iterator (or some other solution) that allows me to do a UNION of several constituent maps. That is, all maps have the same type (or value type and comparator, at least), and I want a single iterator that treats the entire collection as a big multimap (repeated keys are OK) and lets me traverse it in the correct unioned order.

这样的事情是否存在，也许在Boost内？或者是容易装备一个？在伪代码中：

Does such a thing exist, perhaps within Boost? Or is it easy to rig one up? In pseudo code:

std::map<K, M> m1, m2;
union_iterator<K, M> u(m1, m2)
for(auto it = u.begin(); it != u.end(); ++it) { /* ... */ }

例如，如果我们有：

m1 = { { 9:00, "Check in"}, { 12:00, "Break" }, { 16:00, "Check out"} };
m2 = { { 10:30, "coffee" }, { 12:15, "baked beans" }, { 15:00, "lies" } };

然后我想迭代器产生：

9:00, "Check in"; 10:30, "coffee"; 12:00, "Break"; 12:15, "baked beans"; ...

推荐答案

由于宣布，我有一些很酷的东西。

As I announced, I have got something pretty cool.

我现在发布，因为我不知道我是否会回来时间今晚发布。我会花几个字来解释。 （在此后）

I'm posting it now, because I wouldn't be sure whether I'd be back in time tonight to post it. I will be spending a few words in explanation. (in this post)

PS。包含将被修剪掉（约20％我可能会在代码上做一些更一般的工作。

PS. The includes will be trimmed down (to about 20%); I will probably do some more general work on the code too.

很多可以说这个代码：它不是很有效率，而不是很干净（还）。然而，它几乎是无限泛型的，应该像任何其他的。所有代码都可以在github中找到：

A lot can be said about this code: it is not very efficient, and not very clean (yet). It is, however, nearly infinitely generic and should scale like anything else. All code can be found in a github gist:

• merge_maps_iterator.hpp


• Makefile


• test.cpp < a> - 一个相当神秘的测试用例集合，显示一般性_{（我不是说这将是一个好主意要使用ints和float （更不用说同时） - 只是表明它可以完成）}

• merge_maps_iterator.hpp
• Makefile
• test.cpp - a rather arcane set of test-cases showing off the genericity
  _{(I'm not saying that it would be a good idea to have maps keyed with ints and floats (let alone both at the same time) - just showing that it can be done)}

test.cpp，你可以找到它：

Here is the output of the test.cpp as you can find it:

 == input ========================================
{ 2, aap }      { 23, mies }    { 100, noot }   { 101, broer }  
{ b, 3.14 }     
 == output =======================================
     2: aap;
    23: mies;
    98: 3.14;
   100: noot;
   101: broer;

 == input ========================================
{ b, 3.14 }     
{ 2, aap }      { 23, mies }    { 100, noot }   { 101, broer }  
 == output =======================================
     2: aap;
    23: mies;
    98: 3.14;
   100: noot;
   101: broer;

 == input ========================================
{ 2, aap }      { 23, mies }    { 100, noot }   { 101, broer }  
{ 2, aap }      { 23, mies }    { 100, noot }   { 101, broer }  
 == output =======================================
     2: aap;aap;
    23: mies;mies;
   100: noot;noot;
   101: broer;broer;

 == input ========================================
{ b, 3.14 }     
{ b, 3.14 }     
 == output =======================================
     b: 3.14;3.14;

 == input ========================================
{ 1.0, dag }    { 22.0, bye }   { 24.0, Tschüß }
{ 1, true }     { 22, false }   { 24, true }    
{ b, 3.14 }     
{ 2, aap }      { 23, mies }    { 100, noot }   { 101, broer }  
 == output =======================================
   1.0: dag;true;
   2.0: aap;
  22.0: bye;false;
  23.0: mies;
  24.0: Tschüß;true;
  98.0: 3.14;
 100.0: noot;
 101.0: broer;

 == input ========================================
{ 1.0, dag }    { 2.0, EXTRA }  { 22.0, bye }   { 24.0, Tschüß }
{ 1, true }     { 22, false }   { 24, true }    
{ b, 3.14 }     
{ 2, aap }      { 23, mies }    { 100, noot }   { 101, broer }  
 == output =======================================
   1.0: dag;true;
   2.0: EXTRA;aap;
  22.0: bye;false;
  23.0: mies;
  24.0: Tschüß;true;
  98.0: 3.14;
 100.0: noot;
 101.0: broer;

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