Convert a set to a vector of vector - c++

Question

I'm new to C++ and I'm trying to convert unordered_set<string> to vector<vector<int>>
The set contains ("1,2,2","1","1,2","2","2,2"), and each element is a string.
I would like to output a vector<vector<int>> containing
[
[2],
[1],
[1,2,2],
[2,2],
[1,2],
[]
]
So how would I parse each element (string) and make it looks like the above scheme?
#define SSTR( x ) dynamic_cast< std::ostringstream & >( \
( std::ostringstream() << std::dec << x ) ).str()
vector<vector<int> > subsetsWithDup(const vector<int> &num) {
unordered_set<string> result;
for (int i = 0; i < num.size(); i++)
{
result.insert(SSTR(num[i]));
for (int j = i+1; j < num.size(); j++)
{
string d = SSTR(num[i]) + "," +SSTR(num[j]);
result.insert(d);
}
}
string lastString= "";
for (int i = 0; i < num.size(); i++)
{
if ( i == num.size() -1)
{
lastString+= SSTR(num[i]);
}
else
{
lastString+= SSTR(num[i])+",";
}
}
result.insert(lastString);
// convert result back to vector<vector<int>>
return result;
}

Answer 1

If you don't need to validate your strings you can do a transform to construct the vector<vector<int>>:
set<string> foo{ "1,2,2", "1", "1,2", "2", "2,2" };
vector<vector<int>> bar(foo.size());
transform(foo.begin(), foo.end(), bar.begin(), [](const string& i){
vector<int> result;
auto it = const_cast<char*>(i.c_str());
for (result.push_back(static_cast<int>(strtol(it, &it, 10)));
it < i.c_str() + i.size();
result.push_back(static_cast<int>(strtol(++it, &it, 10))));
return result;
});
The lambda in the transform will step through the string:
Start it at the beginning of the string
Using strtol to extract each number
Pushing each number into result
Stepping over each ',' with ++it
Return the constructed result
Prerequisites: This lambda assumes that your input set doesn't contain:
An empty string
A string that begins or ends with a comma (as in "1,2,")
A string that has consecutive commas (as in "1,,2")
That the string contains only contains digits and commas
Note: As a general rule a const_cast is bad so I wanted to comment on why I'm making one. Note that *it is never written to, only it is written to. So this is not violating the const-ness of const string& i. An alternative to strtol that doesn't require a const_cast is stoi, but until we get string_view from C++14 we'll need to construct a new string at each comma, so that's dreadfully inefficient.

Answer 2

One of the possible solution can be:
vector<string> split (string str, string seq) {
vector<string> ret {};
size_t pos {};
while ((pos = str.find (seq)) != string::npos) {
ret.push_back (str.substr (0, pos));
str = str.substr (pos+seq.size ());
}
ret.push_back (str);
return ret;
}
vector<int> to_vec_int (vector<string>&& vec) {
vector<int> ret {};
for (const auto& v : vec) {
ret.push_back (stoi (v));
}
return ret;
}
int main () {
unordered_set<string> st {"1,2,2","1","1,2","2","2,2"};
vector<vector<int>> vec {};
for (const auto& s : st) {
vec.push_back (to_vec_int (split (s, ",")));
}
for (const auto& v : vec) {
for (const auto& s : v) {
cout << s << " ";
}
cout << endl;
}
return 0;
}
Since your elements are delimited by comma, we can split them using split () function and we get vector of strings. This vector has to be converted to vector of int, which is the reason of existence of to_vec_int ().

Answer 3

Here is another possible solution using istringstream to find the commas:
#include <iostream>
#include <string>
#include <vector>
#include <unordered_set>
#include <sstream>
void main()
{
using namespace std;
unordered_set<string> strSet;
strSet.insert("1,2,2");
strSet.insert("1");
strSet.insert("1,2");
strSet.insert("2");
strSet.insert("2,2");
vector<int> nums;
vector<vector<int>> arr_of_nums;
for (const auto &str : strSet) {
istringstream strStream(str);
string strToInt;
while (getline(strStream, strToInt, ',')) {
nums.push_back(stoi(strToInt));
}
arr_of_nums.push_back(nums);
nums.clear();
}
for(const auto &nums : arr_of_nums) {
for (const auto &num : nums) {
cout << num << ",";
}
cout << endl;
}
}