PHP - add values to already existing array - php

Question

I have a already defined array, containing values just like the one below:
$arr = ['a','b','c'];
How could one add the following using PHP?
$arr = [
'a' => 10,
'b' => 5,
'c' => 21
]
I have tried:
$arr['a'] = 10 but it throws the error: Undefined index: a
I am surely that I do a stupid mistake.. could someone open my eyes?
Full code below:
$finishes = []; //define array to hold finish types
foreach ($projectstages as $stage) {
if ($stage->finish_type) {
if(!in_array($stage->finish_type, $finishes)){
array_push($finishes, $stage->finish_type);
}
}
}
foreach ($projectunits as $unit) {
$data[$i] = [
'id' => $unit->id,
'project_name' => $unit->project_name,
'block_title' => $unit->block_title,
'unit' => $unit->unit,
'core' => $unit->core,
'floor' => $unit->floor,
'unit_type' => $unit->unit_type,
'tenure_type' => $unit->tenure_type,
'floors' => $unit->unit_floors,
'weelchair' => $unit->weelchair,
'dual_aspect' => $unit->dual_aspect
];
$st = array();
$bs = '';
foreach ($projectstages as $stage) {
$projectmeasure = ProjectMeasure::select('measure')
->where('project_id',$this->projectId)
->where('build_stage_id', $stage->id)
->where('unit_id', $unit->id)
->where('block_id', $unit->block_id)
->where('build_stage_type_id', $stage->build_stage_type_id)
->first();
$st += [
'BST-'.$stage->build_stage_type_id => ($projectmeasure ? $projectmeasure->measure : '0')
];
if (($stage->is_square_meter == 0) && ($stage->is_draft == 0)) {
$height = ($stage->height_override == 0 ? $unit->gross_floor_height : $stage->height_override); //08.14.20: override default height if build stage type has it's own custom height
$st += [
'BST-sqm-'.$stage->build_stage_type_id => ($projectmeasure ? $projectmeasure->measure * $height: '0')
];
if ($stage->finish_type) {
$finishes[$stage->finish_type] += ($projectmeasure ? $projectmeasure->measure * $height: '0') * ($stage->both_side ? 2 : 1); //error is thrown at this line
}
} else {
if ($stage->finish_type) {
$finishes[$stage->finish_type] += ($projectmeasure ? $projectmeasure->measure : '0');
}
}
}
$data[$i] = array_merge($data[$i], $st);
$data[$i] = array_merge($data[$i], $finishes[$stage->finish_type]);
$i++;
}
The above code is used as is and the array $finishes is the one from the first example, called $arr

Answer 1

You're using += in your real code instead of =. That tries to do maths to add to an existing value, whereas = can just assign a new index with that value if it doesn't exist.
+= can't do maths to add a number to nothing. You need to check first if the index exists yet. If it doesn't exist, then assign it with an initial value. If it already exists with a value, then you can add the new value to the existing value.

Answer 2

If you want to convert the array of strings to a collection of keys (elements) and values (integers), you can try the following:
$arr = ['a','b','c'];
$newVals = [10, 5, 21];
function convertArr($arr, $newVals){
if(count($arr) == count($newVals)){
$len = count($arr);
for($i = 0; $i < $len; $i++){
$temp = $arr[$i];
$arr[$temp] = $newVals[$i];
unset($arr[$i]);
}
}
return $arr;
}
print_r(convertArr($arr, $newVals));
Output:
Array ( [a] => 10 [b] => 5 [c] => 21 )