In PHP arrays works like that:
$a = array("1233", "4345", "3452");
In the above example, the values, "1233", "4345" and "3452" they have each own an index number. So if you run that code:
$a = array("1233", "4345", "3452");
echo "<pre>";
print_r($a);
echo "</pre>";
you will get that result:
Array
(
[0] => 1233
[1] => 4345
[2] => 3452
)
In that case you can't assign an array on "4345" but on "[1]". So, with that in mind if you have another one array like that :
$b = array("321", "654", "987");
and you like to assign it into position "[1]" then you have to do something like that:
$a = array("1233", "4345", "3452");
$b = array("321", "654", "987");
$a[1] = $b;
TAKE CARE
The above code will replace your value "4345" with the content of the array $b. Now let's try to print out your array:
$a = array("1233", "4345", "3452");
$b = array("321", "654", "987");
$a[1] = $b;
echo "<pre>";
print_r($a);
echo "</pre>";
The result will be that now:
Array
(
[0] => 1233
[1] => Array
(
[0] => 321
[1] => 654
[2] => 987
)
[2] => 3452
)
Finaly, if you like to keep both the values "4345" from the array $a and assign an array to that same position into the array $a you have to consider what you like to do with the value "4345"
Some ideas are here:
$a = array("1233", "4345", "3452");
$b = array("321", "654", "987");
$b[] = $a[1];
$a[1] = $b;
echo "<pre>";
print_r($a);
echo "</pre>";
The above code has that result:
Array
(
[0] => 1233
[1] => Array
(
[0] => 321
[1] => 654
[2] => 987
[3] => 4345
)
[2] => 3452
)
Or you can try that:
$a = array("1233", "4345", "3452");
$b = array("321", "654", "987");
$c = array();
$c[] = $a[1];
$c[] = $b;
$a[1] = $c;
echo "<pre>";
print_r($a);
echo "</pre>";
The above code will have the following result
Array
(
[0] => 1233
[1] => Array
(
[0] => 4345
[1] => Array
(
[0] => 321
[1] => 654
[2] => 987
)
)
[2] => 3452
)
"4345 => 12"is easy. But is that really what you want? Can you take a step back and explain what the goal is here?