Changing a Key Value Depending on Another Key Value - php

Question

I have a function like this:
foreach($data as $line) {
if(substr($line,0,1) == "A") {
if(!$first) {
$parts = explode(chr(9),$line);
//echo "<pre>"; print_r($parts); echo "</pre>";
When printed returns multiple arrays like this:
Array
(
[0] => A
[1] => 100_1
[2] => 0
[3] => 1188
[4] => 0
)
Array
(
[0] => A
[1] => 100_2
[2] => 0
[3] => 1188
[4] => 0
)
Array
(
[0] => A
[1] => 100_3
[2] => 0
[3] => 1186
[4] => 0
)
Array
(
[0] => A
[1] => 101_2
[2] => 0
[3] => 1188
[4] => 0
)
Array
(
[0] => A
[1] => 302
[2] => 0
[3] => 1161
[4] => 0
)
Is it possible to 'only' select the keys ([1]) which have values _1,2,3, (if they exist)
and replace the key ([2]) with the same value, so the result would be:
Array
(
[0] => A
[1] => 100_1
[2] => 1
[3] => 1187
[4] => 0
)
Array
(
[0] => A
[1] => 100_2
[2] => 2
[3] => 1188
[4] => 0
)
Array
(
[0] => A
[1] => 100_3
[2] => 3
[3] => 1186
[4] => 0
)
Array
(
[0] => A
[1] => 101_2
[2] => 2
[3] => 1188
[4] => 0
)
Array
(
[0] => A
[1] => 302
[2] => 0
[3] => 1161
[4] => 0
)
I tried to make lots of entries like this but they don't work (I cant get the key right):
foreach($parts as $key => $value) {
if ($value == '100_1') {$parts[$key] = '1';};
if ($value == '100_2') {$parts[$key] = '2';};
if ($value == '100_3') {$parts[$key] = '3';}}
But this would be pure madness as there are over 50 different values and arrays any help would be greatly received.

Answer 1

Something like:
foreach($data as $line) {
if(substr($line,0,1)=="A") {
if(!$first) {
$parts = explode(chr(9), $line);
list($num1, $num2) = explode('_', $parts[1]);
$parts[2] = isset($num2) ? $num2 : $parts[2];
}
}
}