Linear interpolation written as OOP class

class interpolators {

////////////////////////////////////////////////////////////////
///
///         some statistical functons.
///
////////////////////////////////////////////////////////////////
function stat_mean ($data) {
// calculates mean
return (array_sum($data) / count($data));
}

function stat_median ($data) {
// calculates median
sort ($data);
$elements = count ($data);
if (($elements % 2) == 0) {
$i = $elements / 2;
return (($data[$i - 1] + $data[$i]) / 2);
} else {
$i = ($elements - 1) / 2;
return $data[$i];
}
}

function stat_range ($data) {
// calculates range
return (max($data) - min($data));
}

function stat_var ($data) {
// calculates sample variance
$n = count ($data);
$mean = stat_mean ($data);
$sum = 0;
foreach ($data as $element) {
$sum += pow (($element - $mean), 2);
}
return ($sum / ($n - 1));
}

function stat_varp ($data) {
// calculates population variance
$n = count ($data);
$mean = stat_mean ($data);
$sum = 0;
foreach ($data as $element) {
$sum += pow (($element - $mean), 2);
}
return ($sum / $n);
}

function stat_stdev ($data) {
// calculates sample standard deviation
return sqrt (stat_var($data));
}

function stat_stdevp ($data) {
// calculates population standard deviation
return sqrt (stat_varp($data));
}
/////////////////////////end statistical functions///////////////////////////
/////////////should make it in seperate class, i think///////////////////////
/////////////////////////////////////////////////////////////////////////////





/////////////////////////////////////////////////////////////////////////////
//function which returns year and month according to:
//if it is the first day on the month, it returns the current year and month,
//otherwise it returns next month with according year
/////////////////////////////////////////////////////////////////////////////
    function firstFullYearMonth($dateString)
        {
        try {
            $firstDate = new DateTime($dateString);
        }
        catch (Exception $e) {
            echo $e->getMessage();
        exit(1);
        }
                $firstDate= new DateTime($dateString);
                $currentDay=(int) $firstDate->format('d');
                $currentMonth=(int) $firstDate->format('m');
                $currentYear=(int) $firstDate->format('y');
                $prevMonth = (int) date("m", mktime(0, 0, 0, $currentMonth, $currentDay-1, $currentYear));

                if ($currentMonth>$prevMonth)
                    {
                    $firstDay=date("Y-m", mktime(0, 0, 0, $currentMonth, $currentDay, $currentYear));
                    }
                else
                    {
                    $firstDay = date("Y-m", mktime(0, 0, 0, $currentMonth+1, 1, $currentYear));
                    }
        return $firstDay;
    }

/////////////////////////////////////////////////////////////////////////////
//function which returns year and month according to:
//if the date consists of the last day on the month, it returns the current year and month,
//otherwise it returns previous month with according year
/////////////////////////////////////////////////////////////////////////////
    function lastFullYearMonth($dateString)
        {
        try {
            $firstDate = new DateTime($dateString);
        }
        catch (Exception $e) {
            echo $e->getMessage();
        exit(1);
        }
                $firstDate= new DateTime($dateString);
                $currentDay=(int) $firstDate->format('d');
                $currentMonth=(int) $firstDate->format('m');
                $currentYear=(int) $firstDate->format('y');
                $nextMonth = (int) date("m", mktime(0, 0, 0, $currentMonth, $currentDay+1, $currentYear));

                if ($currentMonth<$nextMonth)
                    {
                    $lastDay = date("Y-m", mktime(0, 0, 0, $currentMonth, $currentDay, $currentYear));
                    }
                else
                    {
                    $lastDay = date("Y-m", mktime(0, 0, 0, $currentMonth, 0, $currentYear)); // 0tā diena - iepriekšējā mēneša pēdējā diena.
                    }
        return $lastDay;
    }

/////////////////////////////////////////////////////////////////////////////
//Function interpolates values from 2d array where measurement date is in the first
//dimension and measured value in the second dimension.
//Function returns 2d array with interpolated values for each date between measurements
/////////////////////////////////////////////////////////////////////////////
    function interpolate($arrays)
    {

        $oldDate=$this->firstValDate($arrays);
        $oldVal=$this->firstValVal($arrays);

        next($arrays);

        foreach ($arrays as $key=>$tmpArray)
            {
            $ii=0;
            foreach ($tmpArray as $value)
                {
                    $keys= new DateTime($key);      //try different date formats
                    $keys=$keys->format("Y-m-d");   //compare with standart
                    if ($keys!=$oldDate)
                        {
                        $datums=$keys;
                        $vertiba=$value;

                        $datetimeOld     = new DateTime($oldDate);
                        $datetimeCurrent = new DateTime($datums);

                        $lastForInt = strtotime($oldDate);
                        $firstForInt = strtotime($datums);

                        $intervals = round(($firstForInt-$lastForInt)/60/60/24);
                        if ($intervals<0)
                            {
                            echo "Nākošais datums ir senāks par iepriekšējo.\nLaiks parasti iet uz priekšu un nenāk atpakaļ.";
                            die;
                            }
                        //echo $intervals;

                        $delta=$vertiba-$oldVal;
                        $increment = $delta/$intervals;

                        if ($intervals>1)
                            {
                                for ($i=1;$i<=$intervals;$i++)
                                {
                                    $datetimeOld->modify('+1 day');                     //vecajam datumam pieliek vienu dienu klāt
                                    $currentDay=$datetimeOld->format('Y-m-d');          //pārtaisa datumobjektu uz string
                                    $interpValue=round($oldVal+$increment*$i,2);        //aprēķina patreizējās dienas vērtību pēc formulas
                                                                                        //vecā vērtība plus esošais solis reiz soļa lielums
                                    $interpBoolText=(($i!=$intervals)?"\ti":"");        //visos soļos atrastajai vērtībai galā būs strings "i",
                                                                                        //tas ļauj uzskatāmi redzēt, ka tieši šī vērtība ir interpolēta
                                    $interpArray[$currentDay][$ii]=$interpValue;
                                    $ii++;
                                }
                        $oldDate=$datums;                                               //definējam nākošo "iepriekšējo" datumu un vērtību
                        $oldVal=$vertiba;
                            }
                        else
                            {
                            $interpArray[$datums][$ii]=$vertiba;
                            $oldDate=$datums;
                            $oldVal=$vertiba;
                            $ii++;
                            }

                        }
                    else
                        {
                        $interpArray[$key][$ii]=$value;
                        $ii++;
                        }
                }
            }
            //print_r ($interpArray);
        return $interpArray;
    }


/////////////////////////////////////////////////////////////////////////////
//Returns first key - date value from 2 dimensional associative key array.
//
//
/////////////////////////////////////////////////////////////////////////////
    function firstValDate($arrays)
    {
        foreach ($arrays as $key=>$tempArray)
            {
                return $key;
                break;
            }
    }

/////////////////////////////////////////////////////////////////////////////
//Returns last key - date value from 2 dimensional associative key array.
//
//are there direct way how to get the last key of associative array?
//such loop seems kind of stupid...
/////////////////////////////////////////////////////////////////////////////
    function lastValDate($arrays)
    {
        $i=1;
        foreach ($arrays as $key=>$tempArray)
            {
                if ($i==count($arrays))
                {
                return $key;
                break;
                }
                $i++;
            }
    }

/////////////////////////////////////////////////////////////////////////////
//Returns first key - date value from 2 dimensional associative key array.
//
//
/////////////////////////////////////////////////////////////////////////////
    function firstValVal($arrays)
    {
        return $arrays[$oldDate=$this->firstValDate($arrays)][0];

    }
/////////////////////////////////////////////////////////////////////////////
//Function checks element first two symbols (are they tabs), checks, if the value
//is null or empty and deletes such element.
//
/////////////////////////////////////////////////////////////////////////////
    function unsetEmpty($arrays)
    {
        $i=0;
        foreach($arrays as $key=>$value)
            {
            $rest = substr($value, 0, 2);
            if(!(is_null($value) || $value=="" || $rest=="\t\t"))
                {
                $arrayNew[$i]=$value;
                $i++;
                }
            }
    return $arrayNew;
    }

/////////////////////////////////////////////////////////////////////////////
//Function makes 2 dimensional array from string which is formatted by default
//as "date (tab) value".
//
//should make possibility to divide string in parts and define them (seperator, etc)
//by giving optional parameters.
/////////////////////////////////////////////////////////////////////////////
    function make2dArrayFromDateValueString($dateValueString)
    {
        $text = str_replace("\r", "", $dateValueString);
        $text = str_replace("\n", "+", $text);
        $text = str_replace(",",".",$text);
        $arrtext = explode("+", $text);
        $arrtext=$this->unsetEmpty($arrtext);

        $i=0;
        foreach($arrtext as $key=>$value)
            {
                $bothValues= explode ("\t",$value);
                $datums=$bothValues[0];
                $vertiba=$bothValues[1];
                $masivs2d[$datums][$i]=$vertiba;
                $i++;
            }
        return $masivs2d;
    }

/////////////////////////////////////////////////////////////////////////////
//Function cuts the months which has unfilled daily mesaured values
//
//
/////////////////////////////////////////////////////////////////////////////
    function cutInterpolated($arrays)
        {
        $FirstDateFrom2dArray=$this->firstValDate($arrays);
        $LastDateFrom2dArray=$this->lastValDate($arrays);
        $FirstFullYearMonth=$this->firstFullYearMonth($FirstDateFrom2dArray);
        $LastFullYearMonth=$this->lastFullYearMonth($LastDateFrom2dArray);
        $validDayCount=round((strtotime($LastFullYearMonth."-2")-strtotime($FirstFullYearMonth."-01"))/60/60/24)+1;

        //echo $validDayCount;
        //echo $FirstFullYearMonth;
        //$LastDateFrom2dArray
        if ($validDayCount>0)
            {
                $i=0;
                foreach ($arrays as $key=>$tmpArray)
                {
                    foreach ($tmpArray as $value)
                        {
                        if (($key>=$FirstFullYearMonth) and ($key<=$LastFullYearMonth))
                            {
                            $array[$key][$i]=$value;
                            $i++;
                            }
                        }
                }
            }
        return $array;
        }


/////////////////////////////////////////////////////////////////////////////
//create 2d array with year and month in first dimension and respective
//daily data valuesin seceond
/////////////////////////////////////////////////////////////////////////////
    function createByYearMonth($arrays)
        {
                $k=0;
                foreach ($arrays as $key=>$tmpArray)
                {
                    foreach ($tmpArray as $value)
                        {
                        $currDate=new datetime($key."-01");
                        $Months=(int)$currDate->format("m");
                        if (($oldmonth<$Months) or (($oldmonth==12) and ($Months==1)))                  //skatamies, ja nākamais mēnesis, tad ieliekam iekš masīva
                                {
                                $k=0;
                                $gadsMenesis=$currDate->format("Y-").$oldmonth;
                                $paMenesiem[$currDate->format("Y-m")][$k]=$value;                               //izdala gadu un pareizo mēnesi masīvam
                                $k++;
                                }
                            else
                                {
                                //echo $value;
                                $paMenesiem[$currDate->format("Y-m")][$k]=$value;
                                $k++;
                                }
                                $oldmonth=$Months;

                        }
                }
                //print_r ($paMenesiem);
        return $paMenesiem;
        }
/////////////////////////////////////////////////////////////////////////////
//create 2d array with year and month in first dimension and statistical values
//for respective monthly data in second.
//0 - count
//1 - min
//2 - max
//3 - sum
//4 - average
//5 - median
//6 - variance (for sample)
//7 - variance (for population)
//8 - standart deviation (for sample)
//9 - standart deviation (for population)
/////////////////////////////////////////////////////////////////////////////

    function getStatistics($arrays)
        {
        foreach ($arrays as $key=>$tempone) {
                $array[$key]["count"]=count($tempone);
                $array[$key]["min"]=min($tempone);
                $array[$key]["max"]=max($tempone);
                $array[$key]["sum"]=array_sum($tempone);
                $array[$key]["average"]=stat_mean($tempone);
                $array[$key]["median"]=stat_median($tempone);
                $array[$key]["variance"]=stat_var($tempone);
                $array[$key]["variancep"]=stat_varp($tempone);
                $array[$key]["stdev"]=stat_stdev($tempone);
                $array[$key]["stdevp"]=stat_stdevp($tempone);
                }
            return $array;
        }

}



$interpolators = new interpolators();   //create interpolator object
$masivStrings=$_POST['tabula']; //get some data (date\tvalue\n(\r)) format
$arrays2d= $interpolators->make2dArrayFromDateValueString($masivStrings); //create from gathered data 2dimensional array
$interpolatedArray = $interpolators->interpolate($arrays2d);                //interpolate it daily
$cuttedArray=$interpolators->cutInterpolated($interpolatedArray);           //cut end and last month, if it is not started/lasted from beginning/till end
$paMenesiem=$interpolators->createByYearMonth($cuttedArray);                //sepereate values for each month
$statistika=$interpolators->getStatistics($paMenesiem);                     //get some monthly statistics