Inserting multiple elements into a 2D block - c++

Question

I am attempting to calculate the energy of a series of elements inside a vector of vectors. As soon as the particular element has the right energy, it is then pushed into another vector of vectors. Here is an example because it is hard to explain:
bool energy(const std::vector<double> &vals)
{
float sum = 0.0;
for(unsigned i=0; (i < vals.size()); i++)
{
sum += (vals[i]*vals[i]);
}
//cout << sum << endl;
return (sum >= 5);
}
int main(int argc, char *argv[]) {
std::vector<vector<double> > vals {
{0, 0, 0, 0, 0}, // This has an energy of "0" -> does not count
{1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
{1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
{1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
{1, 2, 1, 1, 1}, //This has an energy of "5" -> push_back to vector[0]
{0, 0, 0, 0, 0}, // This has an energy of "0" -> does not count && start a new
// vector
{1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
{1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
{1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
{1, 2, 3, 4, 5} // This has an energy of "55" -> push_back to vector[1]
};
std::vector<vector<double> > clusters;
std::vector<vector<double> > tmp;
//std::for_each(vals.begin(), vals.end(), energy);
int j = 0;
for(unsigned i=0; (i < vals.size()); i++)
{
if(energy(vals[i]))
{
clusters.resize(j + 1);
clusters[j] = vals[i];
}else if(!energy(vals[i]) && energy(vals[i+1]))
{
j++;
}
}
for(unsigned i=0; (i < clusters.size()); i++)
{
for(unsigned j=0; (j < clusters[i].size()); j++)
{
cout << clusters[i][j] << ' ';
}
cout << endl;
}
}
What should happen
There should be 2 elements of the vector of vectors named clusters each containing the values of:
clusters[0] = {
1, 1, 1, 1, 1,
1, 1, 1, 1, 1,
1, 1, 1, 1, 1,
1, 2, 1, 1, 1
};
`clusters[1] = 1, 2, 3, 4, 5,
1, 2, 3, 4, 5,
1, 2, 3, 4, 5,
1, 2, 3, 4, 5}`
What is happening?
The vector of vectors seem to be over-riding the blocks that get inserted into them. So instead of the above, I just get the last element that it found so:
`cluster[0] = {1 2 1 1 1}
cluster[1] = {1 2 3 4 5}`
What I was thinking and attempting was to store each of the "blocks" inside a vector of vectors that contain the sufficient energy and then push all these values inside a vector<double> and then insert this vector inside the block of clusters..
Is there an alternative way, a much simpler solution to this problem?

Answer 1

Corrected code:
#include<vector>
#include<iostream>
using namespace std;
bool energy(const std::vector<double> &vals)
{
float sum = 0.0;
for(unsigned i=0; (i < vals.size()); i++)
{
sum += (vals[i]*vals[i]);
}
//cout << sum << endl;
return (sum >= 5);
}
int main(int argc, char *argv[]) {
std::vector<vector<double> > vals {
{0, 0, 0, 0, 0}, // This has an energy of "0" -> does not count
{1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
{1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
{1, 1, 1, 1, 1}, // This has an energy of "5" -> push_back to vector[0]
{1, 2, 1, 1, 1}, //This has an energy of "5" -> push_back to vector[0]
{0, 0, 0, 0, 0}, // This has an energy of "0" -> does not count && start a new
// vector
{1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
{1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
{1, 2, 3, 4, 5}, // This has an energy of "55" -> push_back to vector[1]
{1, 2, 3, 4, 5} // This has an energy of "55" -> push_back to vector[1]
};
std::vector<vector<double> > tmp(vals.size());
std::vector<vector<double> > clusters(vals.size());
int j = 0;
for(unsigned i=0; (i < vals.size()); i++)
{
if(energy(vals[i]))
{
clusters[j].insert(clusters[j].end(), vals[i].begin(), vals[i].end());
}else if(!energy(vals[i]) && energy(vals[i+1]))
{
j++;
}
}
for(unsigned i=0; (i < clusters.size()); i++)
{
for(unsigned j=0; (j < clusters[i].size()); j++)
{
cout << clusters[i][j] << ' ';
}
cout << endl;
}
}
The output is:
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

Answer 2

Your problem is here:
for(unsigned i=0; (i < vals.size()); i++)
{
if(energy(vals[i]))
{
clusters.resize(j + 1);
clusters[j] = vals[i];
}
else if(!energy(vals[i]) && energy(vals[i+1]))
{
j++;
}
}
First of all, your energy function returns an int, so when the return value is non-zero, it will evaluate the condition to true, and when it is 0, it will be false.
Second, you are effectively doing a push_back in the if branch, but you are only pushing the current vector (you aren't appending it to an existing vector).
To fix this, I would recommend using a map<int, vector<int>> so you can quickly reference each cluster (e.g. the ones with energy of 5 would have a key of 5, so you would either create a new vector and insert those values, or append to the one that already exists there). If you need it in a vector of vectors, you can always iterate through the map after you have them sorted and swap them into the vector of vectors.

Answer 3

you could simplify a lot your code, so it would be much more easy to read and understand, for example take you energy function, you could write it in a single line using algorithms:
return std::inner_product(vals.begin(), vals.end(), vals.begin(), 0.) >= 5;

Answer 4

I changed a piece of code make it works
int j = 0;
for(unsigned i=0; (i < vals.size()); i++)
{
if(energy(vals[i])) {
clusters[j].insert(clusters[j].end, vals[i].begin(), vals[i].end());
}
if(!energy(vals[i]) && energy(vals[i+1])) {
clusters.push_back( tmp );
++j;
}
}
Don't use resize. You can just push_back an empty vector into your clusters.
And for each operation to append a vector, just using insert by range
void insert (iterator position, InputIterator first, InputIterator last);
Ref: http://en.cppreference.com/w/cpp/container/vector/insert