Is it possible to iterate through a two-dimensional vector of strings and convert the strings into doubles? If so, what would be the best method of doing so? I'm fairly inexperienced with two-dimensional vectors and iterators, so I apologize if this has been asked before. I attempted to find a solution but I didn't have much luck.
This is a small sample of my 2-dimensional vector input:
I attempted to iterate through my two-dimensional vector in the code below in hopes that I could use std::stod() to parse the strings and convert them into doubles, but it didn't work.
// Here is my original vector which I filled by taking input from a csv file
std::vector<std::vector<std::string>> original_matrix;
std::vector<std::vector<double>> doubles_matrix;
doubles_matrix.reserve(original_matrix.size());
for(auto beg = original_matrix.begin(); beg != original_matrix.end(); ++beg)
{
for(auto ceg = beg->begin(); ceg != beg->end(); ++ceg) {
}
}
First of all. There are one million solutions for your problem. Everbody can use what he wants. Styles are different. Newbies generally like C-Style solutions more than sophisticated and "modern C++" solution.
Im my very humble opinion, (only my personal opinion) the answer from user "super" (+1) is by far better as the accepted answer from user "selbie". But OP accepted it and hence, it is the most fitting answer for OP.
I would like to show an additional solution, which is the same as from user "super", just using "more-modern" C++ elements.
You have a 2 dimensional std::vector
. That is a very good approach. Now you want to transform this std::vector
of std::vector
of std::string
into a different data type. You even used the tag "transform" in your question.
For such transformation, you could use a function from the C++ library that has been made for excactly this purpose. It is called std::transform
.
It transforms elements from a container into something different. It iterates over each element in a container and then uses a "function", eg a lambda, to transform that element.
With 2 dimensional vectors, we need to apply std::transform
for each dimension.
And because such a dedicated function is existing in C++, I would recommend to use it.
See the below example:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <iterator>
int main() {
// The source data
std::vector<std::vector<std::string>> vvs{ {"1","2","3","4"},{"5","6","7","8"},{"9","10","11","12"},{"13","14","15","16"}};
// Here we will store the result
std::vector<std::vector<double>> vvd{};
// Transform 2 dimensional vector
// Outer vector
std::transform(vvs.begin(), vvs.end(), std::back_inserter(vvd), [](const std::vector<std::string>&vs) {
std::vector<double> vd{};
// Inner vector
std::transform(vs.begin(), vs.end(), std::back_inserter(vd), [](const std::string& s) { return std::stod(s); });
return vd;
});
// Show debug output
std::for_each(vvd.begin(), vvd.end(), [](const std::vector<double>& vd) {
std::copy(vd.begin(), vd.end(), std::ostream_iterator<double>(std::cout, " ")); std::cout << "\n"; });
return 0;
}
But, as said, everybody can do, what he wants.
#include <vector>
#include <string>
auto convertVector(std::vector<std::vector<std::string>>& stringVec) {
std::vector<std::vector<double>> output;
for (auto& vec : stringVec) {
output.push_back({});
for (auto& str : vec) {
output.back().push_back(std::stod(str));
}
}
return output;
}
Converting a string to double is done with the strtod function:
string s = 3.14;
double d = strtod(s.c_str(), nullptr);
Then apply the above my looping of the vectors any way you want. Here's an example:
void convert(const vector<vector<string>>& stringVectors, vector<vector<double>>& doubleVectors)
{
doubleVectors.clear();
doubleVectors.resize(stringVectors.size());
for (size_t i = 0; i < stringVectors.size(); i++) {
auto& vs = stringVectors[i];
auto& vd = doubleVectors[i];
vd.resize(vs.size());
for (size_t j = 0; j < vs.size(); j++) {
vd[j] = strtod(vs[j].c_str(), nullptr);
}
}
}
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