C++ data structure similar to std::map with multiple key levels

Question

I would like to have a data structure similar to std::map with multiple key levels. For example in this my_map :

(‘a’ , “a1”) ->  “value1”
(‘a’ , “a2”) ->  “value2”
(‘b’ , “b1”) ->  “value3”
(‘b’ , “b2”) ->  “value4”

The first level key values are chars: ['a' and 'b'] and the second key levels are std::string ("a1", etc) and the values are strings.

API requirements:

Adding elements using two key values. Retrieve elements by the first key: my_map.at_first_level('a'), this should return a map like:

"a1" -> “value1”
"a2" -> “value2”

Is this "multi-level map" data structure implemented in any of the C++ libraries?

Take a look at [Boost Multi-index](https://www.boost.org/doc/libs/1_67_0/libs/multi_index/doc/index.html) . — Jesper Juhl, Jun 10 '18 at 16:51
@JesperJuhl I was looking at it right now. It is exactly what I want. — motam79, Jun 10 '18 at 16:55
Seems pretty unclear if you need multi-index container or map of maps. — Öö Tiib, Jun 10 '18 at 17:12

score 7 · Answer 1 · edited Jun 10 '18 at 15:58

7

Have you considered a map of maps ?

std::map<char, std::map<std::string, std::string> myMap;

edited Jun 10 '18 at 15:58

Rakete1111

answered Jun 10 '18 at 15:58

KostasRim

This will work, but if I have more than two levels, the syntax would be cumbersome. I was hoping that someone has implemented a multi-level map similar to Pandas multi-index in C++, where you can lookup values by level number and level key. – motam79 Jun 10 '18 at 16:09
@motam79 If you have multiple levels maybe you are not mapping the problem correctly ? Are you sure you are using the correct data structure for the problem ? – KostasRim Jun 10 '18 at 16:10
@motam79 Could you give an example of the syntax you would prefer in your question? – Galik Jun 10 '18 at 16:25

score 2 · Accepted Answer · answered Jun 10 '18 at 22:45

Here's a recent example I gave using it:

2 Answers2