c++ - Creating 2-D vector with values from another 2-D vector -


i have 2-d vector called cosmic_ray_events has size equal 898281 , created 2-d vector called high-energy_cosmic_rays. put in check in cosmic_ray_elements filters out values less 100 , located @ cosmic_ray_events[i][3]. if value greater 100 transfer elements associated cosmic_ray_event[i][j] 2-d vector or resize current 2-d vector contains vectors had cosmic_ray_events[i][3] greater 100. segmentation fault when try set cosmic_ray_events[i][j] equal 2-d vector. not sure how transfer elements 1 2-d vector without getting segmentation fault.

vector<vector<double> > high_energy_cosmic_rays(he_cr, vector<double>(9,0)); for(int = 0; < cosmic_ray_events.size(); i++) {     if(cosmic_ray_events[i][3] >= 100.)     {         for(int j = 0; j < 9; j++)         {             high_energy_cosmic_rays[i][j] = cosmic_ray_events[i][j];         }     } }

your presizing result vector, isn't possible because have no idea goes in yet. "safe" pre-size use same size original vector, doesn't make sense when you're trying filter them down inner vectors have slot3 content >= 100.

what need start empty vector, , use insertion or push_back add vectors in original vector of vectors target have slot3 >= 100. 1 way using

  • an empty vector of vectors. high_energy_cosmic_rays below.
  • a copy enumeration conditionally copies when expression true item in iteration sequence. std::copy_if can that.
  • an output inserter performs pushback operation. using std::back_inserter wrapped around target vector of vectors object output iterator std::copy_if that.

the results this:

std::vector<std::vector<double>> high_energy_cosmic_rays; std::copy_if(cosmic_ray_events.cbegin(),              cosmic_ray_events.cend(),              std::back_inserter(high_energy_cosmic_rays),              [](std::vector<double> const& v) { return v[3] >= 100; });

unrelated, take care when comparing floating point values.


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