Question

function standard_deviation_population ($a)
{
  //variable and initializations
  $the_standard_deviation = 0.0;
  $the_variance = 0.0;
  $the_mean = 0.0;
  $the_array_sum = array_sum($a); //sum the elements
  $number_elements = count($a); //count the number of elements

  //calculate the mean
  $the_mean = $the_array_sum / $number_elements;

  //calculate the variance
  for ($i = 0; $i < $number_elements; $i++)
  {
    //sum the array
    $the_variance = $the_variance + ($a[$i] - $the_mean) * ($a[$i] - $the_mean);
  }

  $the_variance = $the_variance / $number_elements;

  //calculate the standard deviation
  $the_standard_deviation = pow( $the_variance, 0.5);

  //return the variance
  return $the_standard_deviation;
}

$query_question = mysqli_query($con,"SELECT * FROM question order by s_id");
$QuestionDimArray = array();
while ($data_question = mysqli_fetch_array($query_question))
{
    $QuestionDimArray []= $data_question['q_id'];
}
$a = array($QuestionDimArray());
$standard_deviation = standard_deviation_population ($a);
echo "standard_deviation =" .$standard_deviation;

如何将数据库值存储到

中

$variable = array([database values here]);

例如，定义值（1,2,3）

$a = array(1,2,3);

$standard_deviation = standard_deviation_population ($a);

echo "standard_deviation =" .$standard_deviation;

返回， standard_deviation = 0.81649658092773

Answer 1

以这种方式计算标准偏差并不是一个好主意。数据库系统具有标准偏差的内置函数。您可以在一个查询中获取它，例如：SELECT STDDEV_POP(q_id) FROM question。

在您的代码中，$QuestionDimArray已经是一个数组。你可以$standard_deviation = standard_deviation_population ($QuestionDimArray);

Answer 2

您的问题不明确，但如果我理解得您想将所有数据库结果放入$ variable？

$query_question = mysqli_query($con,"SELECT * FROM question order by s_id");
$QuestionDimArray = array();
while ($data_question = mysqli_fetch_array($query_question)) {
   $QuestionDimArray []= $data_question['q_id'];
   /* if you want the full data line from your query use. It depends your implementation.
      You will have an 2d array
      [['col1' => 'val_line_1_1', 'col2'=> 'val_line_1_2',...],...,['col1' => 'val_line_n_1', 'col2'=> 'val_line_n_2',...]]
   $QuestionDimArray []= $data_question;
   */
}
// $a = array($QuestionDimArray()); unless you want copy the array this line is useless. Event worst its wrong
$standard_deviation = standard_deviation_population ($questionDimArray);
echo "standard_deviation =" .$standard_deviation;

PHP：在数组元素中插入查询结果

2 个答案: