注意：未定义的偏移量：编码2

Question

    Helper.php  
      <script>
            function updateSizes() {
                var sizeString = '';
                for($i = 1; $i <= 12; $i++) {
                    if(jQuery('#size' + $i).val() != '') {
                        sizeString += jQuery('#size' + $i).val() + ':' + jQuery('#threshold' + $i).val() +':'+ jQuery('#threshold'+$i).val() +',';

                    }
                }
                jQuery('#sizes').val(sizeString);
            }
        </script>
    products.php
    if (!empty($sizes)) {
      $sizeString = sanitize($sizes);
      $sizeString = rtrim($sizeString,',');
      $sizesArray = explode(',',$sizeString);
      $sArray = array();
      $qArray = array();
      $tArray = array();
      foreach($sizesArray as $ss){
        $s = explode(':', $ss);
        $sArray[] = $s[0];
        $qArray[] = $s[1];
        $tArray[] = $s[2];
      }
    }
    else
    {
    $sizesArray = array();
    }
    <div class="form-group col-md-2">
                <label for="threshold<?=$i;?>">Threshold:</label>
                <input type="number" name="threshold<?=$i;?>" id="threshold<?=$i;?>"
                value="<?=((!empty($tArray[$i-1]))?$tArray[$i-1]:'');?>" min="0" class="form-control">
              </div>

Notice: Undefined offset: 2  on line sizeString += jQuery('#size' + $i).val() + ':' + jQuery('#threshold' + $i).val() +':'+ jQuery('#threshold'+$i).val() +',';

此行有什么错误 请帮忙 我收到错误，因为未定义偏移量2 什么是未定义偏移量1和未定义的偏移量2以及两者之间的差？