Difference between 2 dates in quarters

Question

I am trying to make a function that gives me the number of quarters between 2 dates as an integer. The dates passed to the function are usually quarter-end dates except occasionally when one of the dates is just an arbitary date.

Basically I want it to figure out what quarter the two dates fall into and give an integer difference in the number of quarters.

E.g.

Q1 2013 -> Q2 2013 = 1
Q1 2013 -> Q4 2013 = 3 
Q2 2012 -> Q2 2013 = 4
Q4 2012 -> Q1 2013 = 1

Here is my function. I realise it is poor and does not return the correct answer all the time but I'm hoping someone can help...

function quarter_diff(DateTime $d1, DateTime $d2){
    //difference in months
    $diff = $d1->diff($d2);

    return ceil((($diff->format('%y') * 12) + $diff->format('%m')+1)/4);
}

and a fiddle here: http://phpfiddle.org/lite/code/tiw-jx3

We can see theat when the date is in the month after the end of a quarter we don not get the correct answer.

Can anyone suggest an improvement??

Answer 1

Convert each of your dates into quarters, then do the math, much like your first example. Some quick pseudocode:

Convert d1 to quarter and year -> d1.quarter and d1.year
Convert d2 to quarter and year -> d2.quarter and d2.year
Number of quarters = d1.quarter - d2.quarter + (d1.year - d2.year)*4

Use the absolute value of the result to get the number of quarters difference.

You can create a quick and dirty "quarter" function by dividing month-1 by 3 and adding 1 to the integer portion of the result. Assuming January = 1, December = 12 and Q1 = January through March. You'll have to make adjustments if Q1 starts elsewhere, such as July.

Q = (int)(month - 1)/3 + 1
or
Q = ceiling(month/3)

Answer 2

This is what I opted for thanks to suggestion from Maple

function quarter_diff(DateTime $d1, DateTime $d2){
    //Returns the number of quarters between two dateTime objects
    if ($d2 > $d1){
        $dtmp = $d1;
        $d1=$d2;
        $d2=$dtmp;
        unset($dtmp);
    }
    $d1q = ceil($d1->format('m')/3);
    $d2q = ceil($d2->format('m')/3);
    $d1y = $d1->format('y');
    $d2y = $d2->format('y');

    return $d1q - $d2q + 4*($d1y - $d2y);
} 

Answer 3

in MYSQL:

SELECT (year('2016-06-30') - year('2015-07-01'))*4 + quarter('2016-06-30') - quarter('2015-07-01') + 1