2D array doesnt show data - php

Question

I have a module in my projects its about the finding free places in the classroom timetable. I am taking variables without problem from database. I need an array which is returns for all classroom which is how many classroom i have in DB. This classrooms also has variable time period 1 till 12 and each period has duration for example if i have in 4th period 3 duration it should write 1 2 3 x x x 7 8 9 10 11 12 and if i have another course in 9th period 2 duration it should be 1 2 3 x x x 7 8 x x 11 12. I did it in 1D array if i give the class_no in query. but it should do it more than a classroom. it shows just numbers 1..12 in 1 line.
$dayy = $_GET['src_day0'];
$drt = $_GET['src_duration0'];
$tm = $_GET['src_time0'];
$faculty_id = $_SESSION['faculty_id'];
$scale = "select DISTINCT t.class_no,t.time,t.duration from ttable t,class c where
day='$dayy' AND (t.faculty='$faculty_id' OR c.faculty='$faculty_id')";
$result = $conn->query($scale);
$x = 1;
while ($rows = $result->fetch_assoc()) {
$class = $rows['class_no'];
$arr = array(
array($x => "$class"),
array(
1 => " 1 ", 2 => " 2 ", 3 => " 3 ", 4 => " 4 ", 5 => " 5 ", 6 => " 6 ",
7 => " 7 ", 8 => " 8 ", 9 => " 9 ", 10 => " 10 ", 11 => " 11 ", 12 => " 12 ",
));
$x++;
}
while ($rows = $result->fetch_assoc()) {
$time = $rows['time'];
$duration = $rows['duration'];
$result1 = ($time + $duration);
for($j=1;$j<$x;$j++)
for ($i = $time; $i < $result1; $i++)
$arr[$j][$i] = "x1";
}
}
for ($i = 1; $i < $x; $i++) {
for ($j = 1; $j < 13; $j++)
echo $arr[$i][$j];
echo "</br>";

Answer 1

In fact you missbuilded your array :)
If your looking your code:
$class = $rows['class_no'];
$arr = array(
array($x => "$class"),
array(
1 => " 1 ", 2 => " 2 ", 3 => " 3 ", 4 => " 4 ", 5 => " 5 ", 6 => " 6 ",
7 => " 7 ", 8 => " 8 ", 9 => " 9 ", 10 => " 10 ", 11 => " 11 ", 12 => " 12 ",
));
$x++;
For each iteration of the loop, you overwrite the array with a new value.
In fact, you need to create a new data and append it on the array.
A way to do it, is the following process:
$arr = [];
while ($rows = $result->fetch_assoc()) {
$arr[ $rows['class_no'] ] = [1 => ' 1 ', 2 => ' 2 ', /*...*/];
}
// free memory if needed
while ($rows = $result->fetch_assoc()) {
for( $i = $rows['time'] ; $i < $rows['time'] + $rows['duration'] ; $i++ ) {
$arr[ $rows['class_no'] ][ $i ] = 'x';
}
}
Here, you create an empty variable $arr of array type. Then, for each data on the loop, you created a new line (for each class_no) with the default values.
On the second loop, you iterate again on the results, but here, you take each array data by class_no and change the correct time value to x