Radio button values in a foreach loop in PHP Codeigniter - php

Question

I am trying to create an input element of type radio within a foreach loop and save the values in a database when the submit button is clicked. I'm using Codeigniter framework.
My views:
<?php echo form_open('students_report/produce_aptitude_score/'.$y->id); ?>
<table>
<tbody>
<?php
$i = 1;
foreach ($aptitudes as $p) { ?>
<input type="hidden" name="aptitude[]" value="<?php echo $p->aptitude; ?>" />
<tr>
<td><?php echo $i; ?></td>
<td><?php echo $p->aptitude; ?></td>
<td>
<div class="form-group">
<input class="form-control" type="radio" name="score[<?php echo $i; ?>]" value="1" />
</div>
</td>
<td>
<div class="form-group">
<input class="form-control" type="radio" name="score[<?php echo $i; ?>]" value="2" />
</div>
</td>
</tr>
<?php $i++; //increment index
} //endforeach ?>
</tbody>
</table>
<button class="btn btn-success btn-lg">Submit</button>
<?php echo form_close(); ?>
My Controller
public function produce_aptitude_score($id) {
$y = $this->common_model->get_student_details_by_id($id);
$this->form_validation->set_rules('aptitude[]', 'Aptitude', 'trim');
$aptitude = $this->input->post('aptitude', TRUE);
$score = $this->input->post('score', TRUE);
if ($this->form_validation->run()) {
for ($i = 0; $i < count($aptitude); $i++) {
$d_aptitude = $aptitude[$i];
$d_score = $score[$i];
$query = $this->students_report_model->check_aptitude_score_exists($id, $d_aptitude);
if ($query->num_rows() == 0) { //data does not exists, do insert
$this->students_report_model->insert_aptitude_score($id, $d_aptitude, $d_score);
} else { //data already exists, do update
$this->students_report_model->update_aptitude_score($id, $d_aptitude, $d_score);
}
}
$this->session->set_flashdata('status_msg', "Aptitude score submitted successfully for {$y->first_name}");
redirect($this->agent->referrer());
} else {
$this->produce_report($id); //form validation fails, reload page with errors
}
}
My Model
public function insert_aptitude_score($id, $aptitude, $score) {
$y = $this->common_model->get_student_details_by_id($id);
$data = array(
'admission_id' => $y->admission_id,
'aptitude' => $aptitude,
'score' => $score,
'session' => current_session,
'term' => current_term,
);
return $this->db->insert('aptitude_scores', $data);
}
public function update_aptitude_score($id, $aptitude, $score) {
$y = $this->common_model->get_student_details_by_id($id);
$query = $this->check_aptitude_score_exists($id, $aptitude);
$result_id = $query->row()->id;
$data = array(
'aptitude' => $aptitude,
'score' => $score,
);
$this->db->where('id', $result_id);
return $this->db->update('aptitude_scores', $data);
}
When I submit, why do I get the following error?
PHP: Undefined offset: 0
Database: Column 'score' cannot be null