PHP - add values to already existing array

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

“I have tried: $arr['a'] = 10 but it throws the error: Undefined index: a” - no it doesn’t: 3v4l.org/7koaV — C3roe
– C3roe, Commented Aug 14, 2020 at 8:43
it does, that's why I am here. And the downvote is just rude.. — rosuandreimihai
– rosuandreimihai, Commented Aug 14, 2020 at 8:43
Writing $arr['a'] = 10 doesn't add value to a that you initialized in the first place. a IS the value of first element in array. If you write a line of code that you said is throwing exception, you'll just add key 'a' with value '10' to array that consists of [0] => 'a', [1] => 'b', .... — Marfee
– Marfee, Commented Aug 14, 2020 at 8:48
You're using += in your real code instead of =. That tries to do maths to add to an existing value, whereas = can just assign the new index if it doesn't exist. It can't do maths to add a number to nothing. You need to check first if the index exists yet. If it doesn't exist, then assign it with an initial value. If it already exists with a value, then you can add the new value to the existing value. — ADyson
– ADyson, Commented Aug 14, 2020 at 8:51
P.Sthe downvote is purely practical, to show the question wasn't clear. You said "I have tried:$arr['a'] = 10" but when we see your real code, we learn that this isn't actually true at all. Details matter in programming. — ADyson
– ADyson, Commented Aug 14, 2020 at 8:54

ADyson · Accepted Answer · 2020-08-14 08:59:17Z

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.

answered Aug 14, 2020 at 8:59

ADyson

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Majed Badawi · Accepted Answer · 2020-08-14 08:49:27Z

0

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 )

answered Aug 14, 2020 at 8:49

Majed Badawi

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