PHP Basic::mean方法代碼示例

 /**
  *  Calculate the outliers for a dataset using
  *  'Standard Deviation around the mean'.
  *  
  *  Steps:
  *  	1. Calculate the mean and the std
  *  	2. Calculate the top and bottom thresholds
  *  	3. It a value is over the top or under the bottom value, 
  *  		then it is an outlier.
  *  
  *  @param array $data
  *  @param number $mean_thres
  */
 public static function outlierAroundMean(array $data, $mean_thres = 2)
 {
     $outliers = [];
     // Step 1.
     $mean = Basic::mean($data);
     $std = Error::std($data);
     // Step 2.
     $top = $mean + $mean_thres * $std;
     $bottom = $mean - $mean_thres * $std;
     // Step 3.
     foreach ($data as $item) {
         if ($item > $top || $item < $bottom) {
             array_push($outliers, $item);
         }
     }
     return $outliers;
 }

 /**
  *  Calculates the 'Simple Moving Average' for a data set.
  *  
  *  Steps:
  *  	1. Make sure elements are numeric
  *  	2. 'Moving Average Value' can't be greater than the size of the elements.
  *  		In such case set the value to the size of the elements.
  *  	3. Calculate the number of the Moving Average calculated elements.
  *  	4. Initiate the array to be returned with null values.
  *  	5. Calculate the Moving Average values:
  *  		1. Calculate new array with the needed elements, based on the given 'Moving Average Value'
  *  		2. Calculate the mean
  *  		3. Add it to the array
  *  
  *  @param number 	$ma_value		Moving Average Value
  *  @param array 	$data			Data Set
  */
 public static function simpleMovingAverage($ma_value, $data = [])
 {
     // Step 1.
     array_map("self::isNumeric", $data);
     // Step 2.
     $ma_value = self::fixMaValue(count($data), $ma_value);
     // Step 3.
     $ma_calc_items = count($data) - $ma_value + 1;
     // Step 4.
     $ma_arr = array_pad([], count($data), null);
     // Step 5.
     for ($i = 0; $i < $ma_calc_items; $i++) {
         // Step 5.1.
         $arr = array_slice($data, $i, $ma_value);
         // Step 5.2.
         $mean = Basic::mean($arr);
         // Step 5.3
         $ma_arr[$i + $ma_value - 1] = $mean;
     }
     return $ma_arr;
 }

 /**
  *  Calculates the variance for a data set for a pupulation or a sample set.
  *  Variance is defined as 'The average of the squared differences from the Mean.'.
  *  
  *  References:
  *  http://www.mathsisfun.com/data/standard-deviation.html
  *  
  *  Steps:
  *  	1. Make sure that elements are numeric
  *  	2. Calculate the mean
  *  	3. Calculate the variance : the 'Mean Squared Error' between the elements and the mean
  *  
  *  @param array $data
  */
 public static function variance($data = [], $population = true)
 {
     $variance = 0;
     // Step 1.
     array_map("self::isNumeric", $data);
     // Step 2.
     $mean = Basic::mean($data);
     // Step 3.
     $n = count($data);
     $sum = 0;
     for ($i = 0; $i < $n; $i++) {
         $sum += pow(self::absoluteError($data[$i], $mean), 2);
     }
     if ($population == true) {
         $variance = round($sum / $n, 3);
     } else {
         $variance = round($sum / ($n - 1), 3);
     }
     return $variance;
 }