Trying to implode multidimensional array joined with $key.$subkey1.$subkey2...$subkeyN = $value - php

Question

I have a small problem with my recursive function, and it is that FQDN is not being created correctly.
public function testBuildReverseSchemaNames() {
$input = [
'propertyZeroSchema' => 'value_0',
'communicationPreferences' => [
'grv3_newsletter_bi' => true
],
'someContainer' => [
'propertyOneSchema' => 'value_1'
],
'propertyThreeSchema' => 'value_3'
];
$expected = [
'propertyZeroSchema' => 'value_0',
'communicationPreferences.grv3_newsletter_bi' => true,
'someContainer.propertyOneSchema' => 'value_1',
'propertyThreeSchema' => 'value_3'
];
$output = [];
$this->buildReverseSchemaNames($input, $output);
$this->assertEquals($expected, $output);
}
public function buildReverseSchemaNames($data, &$output, $currentFqdn = '') {
foreach ($data as $key => $value) {
if (is_array($value)) {
$currentFqdn .= $key.'.';
$this->buildReverseSchemaNames($value, $output, $currentFqdn);
} else {
$currentFqdn .= $key;
$output[$currentFqdn] = $value;
}
}
}
But the output is like this:
Array (
'propertyZeroSchema' => 'value_0'
'propertyZeroSchemacommunicationPreferences.grv3_newsletter_bi' => true
'propertyZeroSchemacommunicationPreferences.someContainer.propertyOneSchema' => 'value_1'
'propertyZeroSchemacommunicationPreferences.someContainer.propertyThreeSchema' => 'value_3'
)

Answer 1

Well, I was able to find the answer by myself:
Edit: After I thought about doing it cleaner, #jh1711 just answered this. If you repost it I will accept your answer.
public function buildReverseSchemaNames($data, &$output, $currentFqdn = '') {
foreach ($data as $key => $value) {
if (is_array($value)) {
$this->buildReverseSchemaNames($value, $output, $currentFqdn . $key.'.');
} else {
$output[$currentFqdn.$key] = $value;
}
}
}

Answer 2

You should not modify $currentFqdn inside your function. Otherwise your changes will affect later iteration of the foreach loop. It should work, if you modify your code like this:
public function buildReverseSchemaNames($data, &$output, $currentFqdn = '') {
foreach ($data as $key => $value) {
if (is_array($value)) {
$this->buildReverseSchemaNames($value, $output, $currentFqdn.$key.'.');
} else {
$output[$currentFqdn.$key] = $value;
}
}
}