What is $unrolled_data?

Here's the function I'm attempting to deconstruct:

protected function pipeToArray($pipe_delim){

        $lines = explode("\n", str_replace("\r\n","\n",$pipe_delim));

        //Subsets of each statement
        $statement = array(
                'statement' => array(),
                'client' => array(),
                'guarantor' => array(),
                'patient' => array(),
                'unrolled_data' => array(),
                'rolled_data' => array(),
                'paymentplan_options' => array(),
                'paymentplan' =>array()
            );

        //Loop through the lines
        foreach ($lines as $raw_line) {

            //Split into cells
            $line = explode("|",$raw_line);

            switch ($line[0]) {
                  case 'N6' :
                    //Unrolled Account Information
                    $index = count($statement['unrolled_data']);
                    foreach($statement['unrolled_data'] as $i => $enc){
                        if($enc['encounterid'] === $line[1]) {
                            $index = $i;
                            continue;
                        }
                    }

                    $statement['unrolled_data'][$index]['txns'][] = array(

                        //'encounterid'   => $line[1],
                        //'provider_name' => $line[2],
                        'date'          => $line[3],
                        'type'          => $line[4],
                        'description'   => $line[5],
                        'amount'        => $line[6]
                        //'left_to_pay'   => $line[7]

                    );


                    break;
                case 'A6' :
                    //Rolled Account Information
                    $statement['rolled_data'][] = array(

                        'encounterid'   => $line[1],
                        'provider'      => $line[2],
                        'description'   => $line[3],
                        'date'          => $line[4],
                        'charged'       => $line[5],
                        'adjustments'   => $line[6],
                        'payments'      => $line[7],
                        'left_to_pay'   => $line[8]

                    );
                    break;
                }
        }
        return $statement;
    }

    /**
     * Return the pdf buffer string
     * @return String pdf buffer
     * @todo THESE ARE BEING HARDCODED TO TEMPLATEIDS... THIS SHOULD BE DONE ELSEWHERE, IN A BUILDER/FACTORY PERHAPS.
     */
    protected function toPDF(){
        if($this->statement_data['statement']['templateid'] == 4) {
            $image = new StandardStatementPDFGenerator($this);
        } else if ($this->statement_data['statement']['templateid'] == 9) {
            $image = new LetterStatementPDFGenerator($this);
        } else {
            //This is a "Fail Gracefully" measure. We haven't generated a statement
            //without a templateid since July 2013, so we shouldn't hit this moving
            //forward.
            $image = new StandardStatementPDFGenerator($this);
        }

        return $image->getStream();

    }

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First part of my question: "unrolled_data" is not a column heading in a table. It is simply the name that's being given to a subset I'm about to create, correct?

Second part of my question: Beginning at line 26, I've got this:

//Unrolled Account Information
                    $index = count($statement['unrolled_data']);
                    foreach($statement['unrolled_data'] as $i => $enc){
                        if($enc['encounterid'] === $line[1]) {
                            $index = $i;
                            continue;
                        }
                    }

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What's going on here?

$index=count($statement['unrolled_data']) // how can you count an array that has yet to be processed?

foreach($statement['unrolled_data'] as $I->$enc){ //where did $enc come from and what's happening here?

For the sake of clarity and brevity, I've attempted to streamline the function that I'm working on. What you see above is a portion of the actual code. I've got that below, just in case there's something missing from the puzzle that you need.

Bottom line: I'm trying to understand how "unrolled_data" is being defined and calculated.

What do you think?