Concise lists/vectors in C++

Question

I'm currently translating an algorithm in Python to C++.

This line EXCH_SYMBOL_SETS = [["i", "1", "l"], ["s", "5"], ["b", "8"], ["m", "n"]] is now

    vector<vector<char>> exch_symbols;

    vector<char> vector_1il;
    vector_1il.push_back('1');
    vector_1il.push_back('i');
    vector_1il.push_back('l');

    vector<char> vector_5s;
    vector_5s.push_back('5');
    vector_5s.push_back('s');

    vector<char> vector_8b;
    vector_8b.push_back('8');
    vector_8b.push_back('b');

    vector<char> vector_mn;
    vector_mn.push_back('m');
    vector_mn.push_back('n');

    exch_symbols.push_back(vector_1il);
    exch_symbols.push_back(vector_5s);
    exch_symbols.push_back(vector_8b);
    exch_symbols.push_back(vector_mn);

I hate to have an intermediate named variable for each inner variable in a 2-D vector. I'm not really familiar with multidimensional datastructures in C++. Is there a better way?

What's happening afterwards is this:

multimap<char, char> exch_symbol_map;

/*# Insert all possibilities
    for symbol_set in EXCH_SYMBOL_SETS:
        for symbol in symbol_set:
            for symbol2 in symbol_set:
                if symbol != symbol2:
                    exch_symbol_map[symbol].add(symbol2)*/
void insert_all_exch_pairs(const vector<vector<char>>& exch_symbols) {
    for (vector<vector<char>>::const_iterator symsets_it = exch_symbols.begin();
        symsets_it != exch_symbols.end(); ++symsets_it) {
            for (vector<char>::const_iterator sym1_it = symsets_it->begin();
                sym1_it != symsets_it->end(); ++sym1_it) {
                    for (vector<char>::const_iterator sym2_it = symsets_it->begin();
                        sym2_it != symsets_it->end(); ++sym2_it) {
                            if (sym1_it != sym2_it) {
                                exch_symbol_map.insert(pair<char, char>(*sym1_it, *sym2_it));
                            }
                    }
            }
    }
}

So this algorithm should work in one way or another with the representation here. The goal is that EXCH_SYMBOL_SETS can be easily changed later to include new groups of chars or add new letters to existing groups. Thank you!

Answer 1

I would refactor, instead of vector<char>, use std::string as internal, i.e.

vector<string> exch_symbols;
exch_symbols.push_back("1il");
exch_symbols.push_back("s5");
exch_symbols.push_back("b8");
exch_symbols.push_back("mn");

then change your insert method:

void insert_all_exch_pairs(const vector<string>& exch_symbols) 
{
  for (vector<string>::const_iterator symsets_it = exch_symbols.begin(); symsets_it != exch_symbols.end(); ++symsets_it) 
  {
    for (string::const_iterator sym1_it = symsets_it->begin();  sym1_it != symsets_it->end(); ++sym1_it) 
    {
      for (string::const_iterator sym2_it = symsets_it->begin(); sym2_it != symsets_it->end(); ++sym2_it) 
      {
        if (sym1_it != sym2_it)
          exch_symbol_map.insert(pair<char, char>(*sym1_it, *sym2_it));
      }
    }
  }
}

Answer 2

You could shorten it by getting rid of the intermediate values

vector<vector<char> > exch_symbols(4, vector<char>()); //>> is not valid in C++98 btw.
//exch_symbols[0].reserve(3)
exch_symbols[0].push_back('i');
etc.

You could also use boost.assign or something similiar
EXCH_SYMBOL_SETS = [["i", "1", "l"], ["s", "5"], ["b", "8"], ["m", "n"]] then becomes vector<vector<char>> exch_symbols(list_of(vector<char>(list_of('i')('1')('l')))(vector<char>(list_of('s')('5'))(list_of('m')('n'))) (not tested and never used it with nested vectors, but it should be something like this)