php array, error when filtering array and the value is not present

Question

I'm trying to use isset to check if the $filtered_data returns a set of data.

I'm using this code rather than foreach because datasetID is a unique id.

My novice understanding is that if (isset($filtered_data)) returns true or false? So the if mrans that if records are returned do x. So, currently when I put in $lastPart = '5fd4058e5c8d2' I'm getting the expected result. When I change the 2 to a 3 (a non-existing ID) $lastPart = '5fd4058e5c8d3' I get Undefined index: 5fd4058e5c8d3`.

I expect the isset is doing its job and the error is thrown on this line as indicated in the error message $filtered_data = array_column(array_merge(...$data), null, 'datasetID')[$lastPart]; am I missing the obvious? I guess this needs a get out clause if the value $lastPart does not exist in the array?

$filtered_data = array_column(array_merge(...$data), null, 'datasetID')[$lastPart];

if (isset($filtered_data)){
  echo 'qwertyuio';
  $datasetID = $filtered_data['datasetID'];
  $collectionCode = $filtered_data['collectionCode'];
  $datasetName = $filtered_data['datasetName'];
  $ownerInstitutionCode = $filtered_data['ownerInstitutionCode'];
  $vernacularName = $filtered_data['vernacularName'];
  $elementName = strtolower($filtered_data['elementName']);
} else {
  echo 'not set';
}

array_column() always returns an array, so $filtered_data will always be set. — Barmar
– Barmar, Commented Dec 16, 2020 at 21:16
@Barmar True, but the OP is attempting to assign an element in that returned array. — user9613905
– user9613905, Commented Dec 16, 2020 at 21:43

Nigel Ren · Accepted Answer · 2020-12-16 21:16:01Z

1

A quick fix would be to use null coalescing (??) and setting the value to a dummy value if not found, then your isset() can be reworked to check for the dummy value...

$filtered_data = array_column(array_merge(...$data), null, 'datasetID')[$lastPart] 
                  ?? null;

if ($filtered_data){

answered Dec 16, 2020 at 21:16

Nigel Ren

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2 Comments

Spatial Digger Over a year ago

great, that works! But you say quick fix is it the best fix, the best way to do this?

Nigel Ren Over a year ago

TBH, without knowing how the data is created, it is a simple fix. IF you could alter the $data array, you could index it by the 'datasetID' column as you load it, then use isset($data[$lastPart])

user9613905 · Accepted Answer · 2020-12-16 21:41:29Z

You're missing the obvious: you're trying to access a non-existent element when you assign it to $filtered_data, so the error occurs there. You're not testing for its existence until the next line.

Try this:

$filtered_data = array_column(array_merge(...$data), null, 'datasetID');
if (isset($filtered_data[$lastPart]) {
  $filtered_data = $filtered_data[$lastPart];
  echo 'qwertyuio';
  $datasetID = $filtered_data['datasetID'];
  $collectionCode = $filtered_data['collectionCode'];
  $datasetName = $filtered_data['datasetName'];
  $ownerInstitutionCode = $filtered_data['ownerInstitutionCode'];
  $vernacularName = $filtered_data['vernacularName'];
  $elementName = strtolower($filtered_data['elementName']);
} else {
  echo 'not set';
}

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