php array : how to access the “$key-1” in an associative array?

Question

i got an existing foreach with a set of conditions , i'd like to keep it as it is and add the end date that is the beginning date of the line before + one day

How could i access to the "$line-1" to do:

foreach($tab as $line){
       if the line before with $line[beginning_date] exists
           $line[end_date]=   the line before with $line[beginning_date] value +1
 }

Answer 1

Good enough?

$theLineBefore = null;
foreach($tab as $line){
       if the line before with $line[beginning_date] exists
           $line[end_date]=   the line before with $line[beginning_date] value +1
  $theLineBefore = $line;
 }