未定义的偏移：3错误excel文件上传和INSERT

I am using below code to upload excel and INSERT in mysql in php

public function read_file($table = 'users', $filename = 'test.xls') {


        $this->load->library('Spreadsheet_Excel_Reader');

        //$data = new Spreadsheet_Excel_Reader($pathToFile);
        $data = new Spreadsheet_Excel_Reader();
         $data->read($filename);

        $sql = "INSERT INTO $table (";

        for($index = 1;$index <= $data->sheets[0]['numCols']; $index++){
            $sql.= strtolower($data->sheets[0]['cells'][1][$index]) . ", ";
        }
        $valuesSQL = '';
        $sql = rtrim($sql, ", ")." ) VALUES ( ";
        for ($i = 2; $i <= $data->sheets[0]['numRows']; $i++) {

            for ($j = 1; $j <= $data->sheets[0]['numCols']; $j++) {
                $valuesSQL .= "\"" . $data->sheets[0]['cells'][$i][$j] . "\"";
                if($j!=$data->sheets[0]['numCols']){
                        $valuesSQL .= ",";
                }
            }
            if($i!=$data->sheets[0]['numRows']){
                $valuesSQL .= "),(";
            }else{
                $valuesSQL .= ")";
            }
        }
        $sqlQuery = $sql . rtrim($valuesSQL);

        return($sqlQuery );
    }

I am getting below error

A PHP Error was encountered

Severity: Notice

Message: Undefined offset: 3

Filename: controllers/userInfo.php

Line Number: 154
A PHP Error was encountered

Severity: Notice

Message: Undefined offset: 3

Filename: controllers/userInfo.php

Line Number: 154

I am using codeigniter php framework.

line number 154 -> $valuesSQL .= "\"" . $data->sheets[0]['cells'][$i][$j] . "\"";

It means either that row 3 doesn't exist, or (more likely) that column "C" is an empty cell in one of the spreadsheet rows. You should test if isset($data->sheets[0]['cells'][$i][$j]) before using it, and set an appropriate NULL value in your SQL if it doesn't.

if isset($data->sheets[0]['cells'][$i][$j]) {
    $valuesSQL .= "\"" . $data->sheets[0]['cells'][$i][$j] . "\""; 
} else {
    $valuesSQL .= 'NULL'; 
}