/**
* Given a dataset, the method calculates the absolute, relative and
* cumulative frequency of each generated class.
*
* @param array $data
*/
public static function frequencyContinuous($data = [])
{
// Make sure that the elements are numeric
array_map("self::isNumeric", $data);
// Count the elements
$items_count = self::countItems($data);
// Get the number of classes
$classes_num = self::getNumberOfClasses($items_count);
// Get the bottom and top ranges
$range_margins = Basic::range($data);
$range = $range_margins->max - $range_margins->min;
// Calculate the group size
$group_size = self::calcGroupSize($range, $classes_num);
// Create the classes
$classes = self::createClasses($range_margins->min, $group_size, $classes_num);
// Calculate the absolute, relative and cumulative frequency of each class
$classes = self::calcFrequencyContinuous($data, $classes);
// Return the classes
return $classes;
}
/**
* Create a function to calculate the exponential regression of a dataset.
*
* @param array $arrayY set of values.
* @return array a function to accept X values and
* return corresponding regression Y values and a coefficient of determination
*/
public static function exponentialRegression($arrayY)
{
$arrayLength = count($arrayY);
$arrayX = Basic::range(1, $arrayLength);
$xSum = Basic::sum($arrayX);
$yLog = array_map('log', $arrayY);
$yLogSum = Basic::sum($yLog);
$xSquaredSum = Basic::sum(array_map('NumbersPHP\\Basic::square', $arrayX));
$xyLogSum = Basic::sum(array_map(create_function('$x, $yLog', 'return $x * $yLog;'), $arrayX, $yLog));
$a = ($yLogSum * $xSquaredSum - $xSum * $xyLogSum) / ($arrayLength * $xSquaredSum - $xSum * $xSum);
$b = ($arrayLength * $xyLogSum - $xSum * $yLogSum) / ($arrayLength * $xSquaredSum - $xSum * $xSum);
$function = create_function('$x', 'if(is_array($x)) {' . 'foreach($x as &$value)' . '$value = exp(' . $a . ') * exp(' . $b . ' * $value);' . 'return $x;' . '}' . 'else ' . 'return exp(' . $a . ') * exp(' . $b . ' * $x);');
return array($function, self::rSquared($arrayY, array_map($function, $arrayX)));
}
