Queryable.php
public function Sum( $Func = null )
	{
		$items = $this->Select( $Func );
		$sum   = 0;

		foreach ( $items as $item ) $sum += $item;

		return $sum;
	}
public function Sum( $Func = null )
	{
		$items = $this->Select( $Func );
		$sum   = 0;

		foreach ( $items as $item ) $sum += $item;

		return $sum;
	}
public function Sum ( $ Func = null ) { $ items = $ this -> Select ( $ Func ) ; $ sum = 0 ; foreach ( $ items as $ item ) $ sum += $ item ; return $ sum ; }
Get sum of sequence

@param string|Closure $Func
@return double
Get sum of sequence