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How to count months that span multiple years

Posted on 2012-09-02
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Last Modified: 2012-10-01
I'm trying to figure out how to count months that span multiple years. I was trying to do it this way:

        $start_ts 	= 	1331245800; //2012-03-08
	$start_ts	=	strtotime(date('Y-m-1',$start_ts));
	
         $stop_ts	=	1362200400; //2013-03-31
       //$stop_ts	=	1359781200; //2013-02-28
       //$stop_ts 	=	1346458500;	//2012-08-31
  
	$num_days	=	date('t',$stop_ts); // how many days are in the month
	$stop_ts	=	strtotime(date('Y-m-'.$num_days,$stop_ts)); // set timestamp for last day of the month that the timestamp falls in.
	
	// Figure out how many months are in the date range
	$start_str	=	date('Y-m-d', $start_ts);
	$stop_str	=	date('Y-m-d', $stop_ts);
	$d1	= new DateTime($start_str);
	$d2	= new DateTime($stop_str);
	$month_count = ($d1->diff($d2)->m); // Months in date range
	
	echo 'Number of Months: '.$month_count;

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But it won't go past 11 months. If I uncomment the $stop_ts for 2013-02-28 it works fine, but if I leave it as is above it shows 0 months. Any ideas? Am I missing something or is this a limitation of the function?

Thanks,
Brian
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Comment
Question by:bacamaro
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7 Comments
 
LVL 16

Accepted Solution

by:
HagayMandel earned 501 total points
ID: 38359585
See the answer here

$d1 = strtotime("2009-09-01");
$d2 = strtotime("2010-05-01");
$min_date = min($d1, $d2);
$max_date = max($d1, $d2);
$i = 0;

while (($min_date = strtotime("+1 MONTH", $min_date)) <= $max_date) {
    $i++;
}
echo $i; // 8

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0
 
LVL 111

Expert Comment

by:Ray Paseur
ID: 38359714
count months that span multiple years
Please give us a plain-language explanation of what you want to achieve here.  We do not need technical details, just the basic facts.  Thanks, ~!Ray
0
 
LVL 60

Assisted Solution

by:Julian Hansen
Julian Hansen earned 498 total points
ID: 38360137
Depends on how accurate you want to be and how you want to handle partial months but here are some ideas.
<pre>
<?php
// Not sure what 
$dt1 = '2012-08-11';
$dt2 = '2008-05-31';

// Get Year,  month, day values for the date
list($y1, $m1, $d1) = explode('-', $dt1);
list($y2, $m2, $d2) = explode('-', $dt2);

// If older date month is higher decrement newer date for the carry
if ($d2 > $d1) {
  // compensate for year boundaries
  if (--$m1 == 0) {
    $y1--;
    $m1 = 12;
  }
}
// If older month is higher compansate by adding some months
if ($m2 > $m1) {
	$m1+=12;
	$y1--;
}
// Work out the months on what is left
$months = ($y1-$y2)*12 + ($m1 - $m2);
echo $months . "\n";

// Alternative method
// Get time in seconds for each date
$t1 = strtotime($dt1);
$t2 = strtotime($dt2);

// 1 day = 86400 seconds
// working on 365.25 days in a year with 12 months gives average
// days per month of 30.3475
// Months = seconds / (86400 * 30.4375)

echo "Seconds: " . ($t1-$t2) . "\n";
echo "Days: " . ($t1-$t2) / 86400 . "\n";

echo "Months: " . ($t1-$t2) / (86400 * 30.4375) . "\n";
?>
</pre>

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LVL 111

Assisted Solution

by:Ray Paseur
Ray Paseur earned 501 total points
ID: 38361079
See http://www.laprbass.com/RAY_temp_bacamaro.php

This seems to test out in a way that appears numerically correct.  Check lines 38-39 to be sure you're getting the answer you want in the narrow edge cases.

<?php // RAY_temp_bacamaro.php
error_reporting(E_ALL);

// REQUIRED FOR PHP 5.1+
date_default_timezone_set('America/Chicago');

// SOME TEST CASES
$data = array
( array( 'lo' => '2012-03-08', 'hi' => '2012-03-07' )
, array( 'lo' => '2012-03-08', 'hi' => '2012-03-31' )
, array( 'lo' => '2012-03-08', 'hi' => '2012-04-01' )
, array( 'lo' => '2012-03-08', 'hi' => '2012-05-23' )
, array( 'lo' => '2012-03-08', 'hi' => '2014-03-31' )
, array( 'lo' => '2012-03-08', 'hi' => '2012-02-01' )
, array( 'lo' => '2012-03-08', 'hi' => '2013-01-30' )
)
;

// RUN THE TESTS
foreach ($data as $lohi)
{
    $cnt = howManyMonths($lohi["lo"], $lohi["hi"]);
    if ($cnt === FALSE)
    {
        echo "<br/>FROM {$lohi["lo"]} TO {$lohi["hi"]} MONTHS ARE OUT OF ORDER";
        continue;
    }
    echo "<br/>FROM {$lohi["lo"]} TO {$lohi["hi"]} WE COUNT $cnt MONTHS";
    echo PHP_EOL;
}

function howManyMonths($lo, $hi)
{
    $lo = date('Y-m-01', strtotime($lo));
    $hi = date('Y-m-01', strtotime($hi));
    if ($lo > $hi) return FALSE;

    // DECIDE IF DATES IN THE SAME MONTH SHOULD RENDER ZERO MONTHS OR ONE MONTH
    $cnt = 0;
    while ($lo < $hi)
    {
        $cnt++;
        $lo = date('Y-m-01', strtotime("$lo + 1 MONTH"));
    }
    return $cnt;
}

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HTH, ~Ray
0
 
LVL 60

Expert Comment

by:Julian Hansen
ID: 38449914
Why the rating of Good - have you read the rating guide - what in the solutions above did not answer your question?
0
 
LVL 111

Expert Comment

by:Ray Paseur
ID: 38450476
Please see http://www.experts-exchange.com/help/viewHelpPage.jsp?helpPageID=26

Given a tested and working code sample, it seem strange that you would mark the grade down.  Please explain what you expected that you did not get here, thanks. ~Ray
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