C++ Equivalent of Python List of Dictionaries?

Question

I have a Python list of dictionaries that contain information about individual layers of a neural network. Each dictionary can have any number of entries, including more dictionaries.

layer_config = [
 {'conv_layer': {
     'filter_size' : 5,
     'stride' : 1,
     'num_filters' : 20}},
 {'pool_layer': {
     'poolsize' : (2,2)}},
 {'fc_layer': {
     'num_output' : 30}},
 {'final_layer': {
     'num_classes' : 10}}
]

I am converting the program into C++ and need to find a way to organize this information in a similar manner. Are C++ nested maps the best way to accomplish this, or is there another data structure out there that might be a better alternative?

You would have to determine the map types. It's not clear from your example. — Anon Mail, May 15 '17 at 19:52
From your example it's even unclear why that is a list in the first place - to me it looks like it should just be a single dictionary — UnholySheep, May 15 '17 at 19:52
It's very difficult to recommend anything based on a small example – is that structure fixed or can there be more or fewer or different layers? — molbdnilo, May 15 '17 at 19:53
In this case, "best" would be "simplest" in terms of inserting/accessing data — nlhenderson17, May 15 '17 at 19:53
See: http://stackoverflow.com/questions/7804955/heterogeneous-containers-in-c — B. Szablak, May 15 '17 at 20:20

score 5 · Accepted Answer · answered May 15 '17 at 20:08

In C++, to use nested maps for this problem, each map would have to be of the same type. If you created a map of maps, the submaps would all have to hold the same type of information (like strings and ints), and it appears that you have different information being held in your dictionary depending on the key, (i.e you have a pair (2,2) at key "poolsize", where elsewhere you have integers). The C++ way to do this could be to create a struct or class which holds this information. For instance, you could create a struct with four maps for your conv_layer, pool_layer and so on. From your example, it looks like your data structure only needs one map for conv_layer, and a bunch of pairs for all of the other variables. If this is the case, you could use something like this for your data structure:

struct layer_config{
        std::map<std::string, int> conv_layer;
        std::pair<std::string, std::pair<int, int>> pool_layer;
        std::pair<std::string, int> fc_layer;
        std::pair<std::string, int> final_layer;
};

score 3 · Answer 2 · answered May 15 '17 at 20:09

You can use a c++ map, which is similar to the python dictionary, and a vector:

vector<map<string, map<string, int> > >neural_data;
map<string, map<string, int> >regular_data;
regular_data["conv_layer"]["filter_size"] = 5;
neural_data.push_back(regular_data);
cout << neural_data[0]["conv_layer"]["filter_size"]<< endl;

You can then loop through and assign the rest of your data

C++ Equivalent of Python List of Dictionaries?

2 Answers2

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