How to convert multidimensional array to string - php

Question

I have a requirement to gather all the comments of posts and show them in CSV.
For that, I have this kind of array ( post-wise ) :
[21069] => Array
(
[0] => Array
(
[comment_author] => author1
[comment_content] => for testing
)
[1] => Array
(
[comment_author] => author2
[comment_content] => this is
)
[2] => Array
(
[comment_author] => author3
[comment_content] => good
)
)
[21070] => Array
(
[0] => Array
(
[comment_author] => author4
[comment_content] => file reading
)
[1] => Array
(
[comment_author] => author5
[comment_content] => hi
)
)
I want to show this data in CSV , for that, I need to convert the array into a string in this form.
[0]=>Array
(
['author_comment']=>'author1:for testing|author2:this is|author3:good'
)
[1]=>Array
(
['author_comment']=>'author4:file reading|author5:hi'
)
I am not getting how do I use implode function.
EDIT 1 : Please find var_export in below code.
$newArray = [
'21069' => [
'0' => [
'comment_author' => 'author1',
'comment_content' => 'for testing'
],
'1' => [
'comment_author' => 'author2',
'comment_content' => 'this is'
],
'2' => [
'comment_author' => 'author3',
'comment_content' => 'good'
],
],
'21070' => [
'0' => [
'comment_author' => 'author4',
'comment_content' => 'file reading'
],
'1' => [
'comment_author' => 'author5',
'comment_content' => 'hi '
],
],
];

Answer 1

I Manage to concat the comments using below code.
$new1Array = [];
foreach($newArray as $key => $value){
foreach($value as $value1) {
$new1Array[$key][]['author_comment'] = $value1['comment_author'].':'.$value1['comment_content'];
}
}
$finalArraynew = [];
foreach($new1Array as $key => $value) {
$finalArraynew[$key][] = implode('|', array_map(function ($entry) {
return $entry['author_comment'];
}, $value));
}