Why does this work?

Here's the code:

<?php
$data['timeline'] = array();
$txnGroup = array();

$michelle=array(
array("eventdate"=>"2016-08-26", "eventtype"=>"transaction", "runningbal"=>"21.50"),
array("eventdate"=>"2016-08-26", "eventtype"=>"transaction", "runningbal"=>"32.50"),
array("eventdate"=>"2016-08-27", "eventtype"=>"transaction", "runningbal"=>"32.50"),
array("eventdate"=>"2016-08-27", "eventtype"=>"statement", "runningbal"=>"50.50"),
);

 for ($i=0; $i < count($michelle); $i++) {
	$event = $michelle[$i];
	//var_dump($event);
	if($event['eventtype']=='transaction')
	{
		$thisDate = Date('mdy', strToTime($event['eventdate']));
		$nextDate = (isset($michelle[$i+1])&&$michelle[$i+1]['eventtype']=='transaction')?Date('mdy', strToTime($michelle[$i+1]['eventdate'])):null;
		array_push($txnGroup, $event);
		//var_dump($event);
		if ($thisDate <> $nextDate) {
			//add to data
			if (count($txnGroup)!=1) {
				echo "yes";
				array_push($data['timeline'], array(
					'eventdate'=>Date('m/d/Y', strToTime($event['eventdate'])),
					'eventtype'=>'payments',
					'runningbal'=>$event['runningbal'],
					'payments'=>$txnGroup
				));
				 

			} else {
				//this is where you left off. You've got to figure out how to 
				array_push($data['timeline'], $event);
			}
			$txnGroup = array();
		}
	} 
	else 
	{
		array_push($data['timeline'], $event); //anything that's not a transaction event type gets put into the $data['timeline'] array as a regular $event
	}
 }
 var_dump($data['timeline']);
 
 foreach($data['timeline'] as $data)
 {
	echo $data['eventtype'].'<br>';
 }
 echo "<br>";
 //var_dump($txnGroup);

 

?>

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Here's a screen shot of the results:

why
Perfect!

Basically, I need an array within an array when I've got a group of arrays that have the same date.

Awesome!

But I do not understand how by looking at the date of the next array, determining that the current date and the next date don't match, you can wind up with the "payments" array.

Here comes array #1: array("eventdate"=>"2016-08-26", "eventtype"=>"transaction", "runningbal"=>"21.50"),

I'm looking at the date of the next array which is 2016-08-26. They're the same, so I'm going to add this to the $txnGroup array and finish.

Here comes array #2: array("eventdate"=>"2016-08-26", "eventtype"=>"transaction", "runningbal"=>"32.50"),

I'm looking ahead and the dates are NOT the same, so I'm going to move ahead, the current $txnGroup is equal to "1," so...

Bottom line: There's a flow that results in a grouping of transactions that have the same date. It's like a digital version of "Mouse Trap," and while I'm watching it work, I get lost.

How is this working?
brucegustPHP DeveloperAsked:
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Julian HansenConnect With a Mentor Commented:
The result has the last transaction for a date as the parent.
If there is more than 1  transaction for a particular date then the payments member contains the history of all transactions on that date - if there is only 1 payment on a date there is no history - I guess because the root record is self explanatory.

Therefore the != 1 is there to check if a payments element should be created or not.

Another way of looking at
Find a record
Add it to txnGroup - we know we can do this because we check later to see if records are different and reset the array (line 37)
No we get to the date check - which means push into the timeline - but we have two cases
1. There is only one payment on the day
2. There is more than one
If there is one - we don't want to add a payments member - we only want to add the transaction
If there is more than one then we want to set the parent to the data of the most recent transaction and add the history under payments.
This is where the != 1 comes in. There will never be 0 line 19 makes sure of that.
If it is 1 it means we only had 1 transaction for the day - so don't make a payments member
If it is != 1 it actually means > 1 so that means create a payments member.
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Ray PaseurCommented:
Bruce: Please use var_export() to capture the output that is currently posted in image form.  Please post that here in the code snippet, thanks.
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Julian HansenCommented:
From what I can see the code is gatthering transactions for a day and putting them into a payments array which is added to the timeline.

The code does a pre-add - in other words it adds the current item to the txnGroup array and then checks to see if the next transaction also belongs - if it does not - it means it is time to close this group off - so it creates the payment entry and then resets and the next transaction becomes part of a new group.

Not sure if that addresses the question?
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Ray PaseurCommented:
Not sure I understand the question either!  What kind of output are you looking to create from the data in the $michelle array?
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brucegustPHP DeveloperAuthor Commented:
The output that I'm getting is exactly what's supposed to happen. I'm not trying to correct anything. The end result that you see is exactly as it should be. I just don't understand WHY it works.

The first two arrays have the same date and they correctly find themselves in the "payments" array. How? I don't get how by looking ahead to see if the date is different and the current $txnGroup array is not "1," that the first two arrays are grouped together. They should be and they are. But I don't understand how those first two IF clauses can produce that anomaly.
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brucegustPHP DeveloperAuthor Commented:
Ray, here is the $michelle array when I do a var_dump:

array (size=4)
  0 => 
    array (size=3)
      'eventdate' => string '2016-08-26' (length=10)
      'eventtype' => string 'transaction' (length=11)
      'runningbal' => string '21.50' (length=5)
  1 => 
    array (size=3)
      'eventdate' => string '2016-08-26' (length=10)
      'eventtype' => string 'transaction' (length=11)
      'runningbal' => string '32.50' (length=5)
  2 => 
    array (size=3)
      'eventdate' => string '2016-08-27' (length=10)
      'eventtype' => string 'transaction' (length=11)
      'runningbal' => string '32.50' (length=5)
  3 => 
    array (size=3)
      'eventdate' => string '2016-08-27' (length=10)
      'eventtype' => string 'statement' (length=9)
      'runningbal' => string '50.50' (length=5)

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brucegustPHP DeveloperAuthor Commented:
BAM!
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