Loop and AND conditional clause - php

Question

I have had a hard time to get my head around this little piece of code.
protected function compressLowest($lowest){
$result = array();
$result['morning'] = array();
$result['afternoon'] = array();
$result['evening'] = array();
$result['allDay'] = array();
$type = $this->prices->getCondType();
$lastDate = 0;
$i = array();
$i['morning'] = $i['afternoon'] = $i['evening'] = $i['allDay'] = 0;
foreach($lowest as $date => $prices){
foreach($prices as $range => $price) {
if($this->isNextDay($date, $result[$range][$i[$range]]['to']) && $result[$range][$i[$range]]['price'] == $price){
$result[$range][$i[$range]]['to'] = $date;
} else {
$i[$range] = count($result[$range]);
$result[$range][] = array();
$result[$range][$i[$range]]['from'] = $date;
$result[$range][$i[$range]]['to'] = $date;
$result[$range][$i[$range]]['price'] = $price;
$result[$range][$i[$range]]['destime']=$this->arr['destime'];
$result[$range][$i[$range]]['deptime']=$this->arr['deptime'];
$result[$range][$i[$range]]['flight']=$this->arr['flight'];
}
}
$lastDate = $date;
}
//print_r($result);exit();
return $result;
}
And IsNextDay is checked as follows
protected function isNextDay($next, $day){
if($next - $day == 86400){ //60*60*24 = 86400
return true;
} else {
return false;
}
}
I can't figure out what is
isNextDay($date, $result[$range][$i[$range]]['to']) && $result[$range][$i[$range]]['price'] == $price) supposed to mean (the $day thing)?
in the if conditional clause of the second for-loop in the above function. Thank you if you could help me understand.
UPDATE
*Sorry I hadn't read it carefully until I discovered there was ) after the result[][]['to']... thanks for your concern.*
For the source code above, I always have a notice of UNDEFINED OFFSET 0. How to fix this bug-to-be ?

Answer 1

for your Undefined Offset 0 at the if line some index evaluates to 0 and the array you are using that index on does not have an element at that index.
For instance (I won't list all the possibilities) if $range is 0 and $result[0] is non-existent.