Merge multi-dimensional arrays and sum column values which share a common value in another column

问题

I have 3 arrays for storing posts,comments, and likes.

These are the JSON strings:

//comments JSON (stores user and comment points)

$comments='[
    {
        "user": "5",
        "points": "12"
    },
    {
        "user": "2",
        "points": "1"
    },
    {
        "user": "3",
        "points": "1"
    }
]';

//likes(stores user and likes point)

$likes='[
    {
        "user": "1",
        "points": 7
    },
    {
        "user": "4",
        "points": 4
    },
    {
        "user": "3",
        "points": 1
    }
]';

//posts (stores user and post points)

$posts='[
    {
        "user": "1",
        "points": "6"
    },
    {
        "user": "3",
        "points": "2"
    },
    {
        "user": "2",
        "points": "1"
    }
]';

I convert these JSONs into arrays like this:

$comment_array  =   json_decode($comments,TRUE); 
$like_array     =   json_decode($likes,TRUE); 
$post_array     =   json_decode($posts,TRUE); 

//echo '<pre>';
//print_r($comment_array);
//print_r($like_array);
//print_r($post_array);
//echo '</pre>';

Now, I'm trying to sum these points and save the result in a new array. It's not mandatory that a user should have entries in all the three arrays. It depends on whether a user has made a comment, post or like.

function mergeArrays($filenames, $titles, $descriptions) {
    $result = array();

    foreach ( $filenames as $key=>$name ) {
        $result[] = array( 'filename' => $name, 'title' => $titles[$key], 'descriptions' => $descriptions[ $key ] );
    }

    return $result;
}

The above function can merge all the three arrays.

$merged= mergeArrays($comment_array, $like_array, $post_array);

echo '<pre>';
print_r($merged);
echo '</pre>';

However, each array after merging is stored as an index element.

How can I get a result something like this:

$result='[
    {
        "user": "1",
        "points": "13"
    },
    {
        "user": "2",
        "points": "2"
    },
    {
        "user": "3",
        "points": "4"
    },
    {
        "user": "4",
        "points": "4"
    },
    {
        "user": "5",
        "points": "12"
    }
]';

回答1:

Considering your three arrays, this code will get you an array with: points, votes and diferent users.

Edit: Adding additional array and printing it to get the output desired by question.

$points = 0;

$uniqueUsers = array();
$votes = 0;
$users = 0;

$result = array();

//Comments
if (!empty($comment_array)) {
    foreach ($comment_array as $item) {

        if (!in_array($item['user'], $uniqueUsers)) {
            array_push($uniqueUsers, $item['user']);
            $result[$item['user']] = 0;
        }
        $votes ++;
        $result[$item['user']] += $item['points'];
    }
}

// Likes
if (!empty($like_array)) {
    foreach ($like_array as $item) {

        if (!in_array($item['user'], $uniqueUsers)) {
            array_push($uniqueUsers, $item['user']);
            $result[$item['user']] = 0;
        }
        $votes ++;
        $result[$item['user']] += $item['points'];
    }
}

// Posts
if (!empty($post_array)) {
    foreach ($post_array as $item) {

        if (!in_array($item['user'], $uniqueUsers)) {
            array_push($uniqueUsers, $item['user']);
            $result[$item['user']] = 0;
        }
        $votes ++;
        $result[$item['user']] += $item['points'];

    }
}


foreach ($result as $idUser=>$points) {
    echo "\n";
    echo "\n" . 'User: ' . $idUser;
    echo "\n" . 'Points: ' . $points;
}


$results = array('users'=> count($uniqueUsers), 'votes'=>$votes, 'points'=> $points);

//print_r($results);

回答2:

The solution using array_column, array_walk_recursive and array_values functions:

...
$comments = array_column($comment_array, 'points', 'user');
$likes = array_column($like_array, 'points', 'user');
$posts = array_column($post_array, 'points', 'user');

$list = [$comments, $likes, $posts];
$result = [];

array_walk_recursive($list, function($v, $k) use(&$result){
    if (key_exists($k, $result)){
        $result[$k]['points'] += $v;
    } else {
        $result[$k] = ['user' => $k, 'points' => $v];
    }
});
$result = array_values($result);

print_r($result);

The output:

Array
(
    [0] => Array
        (
            [user] => 5
            [points] => 12
        )

    [1] => Array
        (
            [user] => 2
            [points] => 2
        )

    [2] => Array
        (
            [user] => 3
            [points] => 4
        )

    [3] => Array
        (
            [user] => 1
            [points] => 13
        )

    [4] => Array
        (
            [user] => 4
            [points] => 4
        )
)

回答3:

Do the following to get one array with summed points:

$collections = array(
    'comments' => json_decode($comments,TRUE),
    'likes' => json_decode($likes,TRUE);,
    'posts' => json_decode($posts,TRUE),
);

$newArray = array();

foreach ($collections as $collection) {
    foreach ($collection as $user) {
        $newArray[$user->user] += $user->points;
    }
}

回答4:

There are two important points to make if you want to learn the "best" way to handle these types of operations.

Don't use iterated in_array() calls when isset() can be used instead. This is because isset() is much more efficient than in_array().
Use temporary keys to identify duplicate occurrences, then re-index your results when finished -- usually with array_values(), but this time I used array_multisort() to re-order the results AND re-index.

Code: (Demo)

$merged = array_merge(json_decode($comments, true), json_decode($likes, true), json_decode($posts, true));
$result = [];
foreach ($merged as $entry) {
    if (!isset($result[$entry['user']])) {
        $result[$entry['user']] = $entry;
    } else {
        $result[$entry['user']]['points'] += $entry['points'];
    }
}
array_multisort(array_column($result, 'user'), $result);
// usort($result, function($a, $b) { return $a['user'] <=> $b['user']; });  
// array_multisort() will outperform `usort()` in this case.
echo json_encode($result);

Output:

[{"user":"1","points":13},{"user":"2","points":2},{"user":"3","points":4},{"user":"4","points":4},{"user":"5","points":"12"}]

Decode each array and merge them together into a multi-dimensional array.
Iterate each subarray and determine if it is the first occurrence of the user. If so, retain the entire subarray. If not, only increase the points tally within that subarray.
When the loop is finished, sort by user ascending.

This is clean, direct, and readable.

来源：https://stackoverflow.com/questions/37592427/merge-multi-dimensional-arrays-and-sum-column-values-which-share-a-common-value

标签

php

json

multidimensional-array

sum

array-merge