How can I merge these two JSON arrays?

Question

My php generates two JSON arrays like:

[{"category":183,"private_review_ids":[63,59,62]},
{"category":363,"private_review_ids":[331]}, 
{"category":371,"private_review_ids":[341]},
{"category":379,"private_review_ids":[350]}]
[{"category":363,"public_review_ids":[331]},
{"category":373,"public_review_ids":[343]},
{"category":384,"public_review_ids":[356]},
{"category":183,"public_review_ids":[347]}]

How could I merge these arrays so they are just one array of the form below. It is not simply merging the arrays - it is the possible tranferring of the value from one key (public_review_ids) to another key (private_review_ids) within the JSON Object. Here's the form I want the JSON Array:

[{"category":183,"private_review_ids":[63,59,62],"public_review_ids":[347] },
{"category":363,"private_review_ids":[331],"public_review_ids":[]}, 
{"category":371,"private_review_ids":[341],"public_review_ids":[]},
{"category":379,"private_review_ids":[350]},"public_review_ids":[]},
{"category":373,"private_review_ids":[],"public_review_ids":[343]},
{"category":384,"private_review_ids":[],"public_review_ids":[356]}]

As you can see, if the value is in both private_review_ids and public_review_ids, it should appear in just the private_review_ids key.

I tried using array_unique and array_merge but I was having no success, really.

Here's my code:

<?php
require('myfile.php');

    //here is the user_id, which is the corresponding user_id for username +5555555

$user_id = "21";
//Select all related info in the review_shared table 
//where the contact_id column is equal to $user_id.

//a value in the contact_id column means a review is shared with a person, $user_name,
//who owns that number, $user_id
$sql = "SELECT * FROM review_shared WHERE contact_id = ?";
$stmt2 = $con->prepare($sql) or die(mysqli_error($con));
$stmt2->bind_param('i', $user_id) or die ("MySQLi-stmt binding failed ".$stmt2->error);
$stmt2->execute() or die ("MySQLi-stmt execute failed ".$stmt2->error);
$result2 = $stmt2->get_result();

//fetch all rows associated with the respective contact_id value
//in review_shared table
while ($row = $result2->fetch_assoc()) {

    //get the corresponding cat_id in the row
    $cat_id = $row["cat_id"];

    //get the corresponding review_id in the row
    $review_id = $row["review_id"];
    //make an array called $results
    $results[$row['cat_id']][] = $review_id; 

}

$jsonData = array_map(function($catId) use ($results) {
    return [
        'category' => $catId,
        'private_review_ids' => $results[$catId],
        ];
}, array_keys($results));
echo json_encode($jsonData);


    //**********************

//select all rows where public_or_private column = 2
//in review table
$sql2 = "SELECT * FROM review WHERE public_or_private = 2";
$result2 = mysqli_query($con,$sql2);

    //fetch all associated rows where public_or_private column = 2
    while ($row = $result2->fetch_assoc()) {

    //get the corresponding review_id in the row
    $review2_id = $row["review_id"];

    //get the corresponding cat_id in the row
    $cat2_id = $row["cat_id"];

    //make an array called $results
    $results2[$row['cat_id']][] = $review2_id;              

    }

    $jsonData2 = array_map(function($cat2Id) use ($results2) {
    return [
        'category' => $cat2Id,
        'public_review_ids' => $results2[$cat2Id],
        ];
}, array_keys($results2));
echo json_encode($jsonData2);


?>

Answer 1

If you refactor your code, you can remove the need for iterating over the data 4 times (twice each) by immediately appending the query results into your desired data structure.

If you execute your public and private review queries, such that their results are in variables $publicReviews and $privateReviews then:

<?php

// Public and private review query results
$publicReviews = $stmt1->get_result();
$privateReviews = $stmt2->get_result();

// Prepare combined reviews array
$reviews = [];

// Iterate through private review results and append to combined reviews
while (($row = $privateReviews->fetch_assoc())) {
    $category_id = $row['cat_id'];
    $review_id = $row['review_id'];

    $reviews[$category_id]['category'] = $category_id;
    $reviews[$category_id]['private_review_ids'][] = $review_id;
    $reviews[$category_id]['public_review_ids'] = [];
}

// Iterate through public review results and append to combined reviews
while (($row = $publicReviews->fetch_assoc())) {
    $category_id = $row['cat_id'];
    $review_id = $row['review_id'];

    $reviews[$category_id]['category'] = $category_id;

    // Create empty private reviews array, where it doesn't exist
    if (! isset($reviews[$category_id]['private_review_ids'])) {
        $reviews[$category_id]['private_review_ids'] = [];
    }

    // Add review id to public reviews where it doesn't exist in private reviews
    if (! in_array($review_id, $reviews[$category_id]['private_review_ids'])) {
        $reviews[$category_id]['public_review_ids'][] = $review_id;
    }
}

echo json_encode(array_values($reviews));