PHP compare array results and filter

Question

I have a php array that looks like this:

Array(
[3086] => Array
    (
        [id] => 3086
        [note] => Make text larger
        [revision] => 1
        [noteParentId] => 1706
    )

[3087] => Array
    (
        [id] => 3087
        [note] => Make text larger
        [revision] => 2
        [noteParentId] => 1706
    )

[3085] => Array
    (
        [id] => 3085
        [note] => Enlarge this image
        [revision] => 1
        [noteParentId] => 1705
    )

[3084] => Array
    (
        [id] => 3086
        [note] => Another test note
        [revision] => 1
        [noteParentId] => 1704
    )

)

How can I filter it in such a way that if the [noteParentId] has the same value (as seen in [3086] and [3087]), then remove the one with the lower [revision] value from the array?

itoctopus · Accepted Answer · 2015-10-06 19:40:30Z

2

You should sort the array

function mysort($a, $b){
    if ($a['revision'] >= $b['revision'])
        return 1;
    return -1;
}

and then store the matching values in another array

$arrResult = array();
usort($arrTest, "mysort");
foreach ($arrTest as $key=>$value){
    if (!isset($arrResult[$value['noteParentId']]))
        $arrResult[$value['noteParentId']] = array($key=>$value);
}

Now you will need to sanitize $arrResult...

answered Oct 6, 2015 at 19:40

itoctopus

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Comments

Travis · Accepted Answer · 2015-10-06 22:28:55Z

This answer will require a little more code than the previous answers, but I think it's a more efficient solution for the following reasons:

It will always be a O(n) solution for you
It keeps the same data structure you expected
It won't require you to merge multiple filtered result sets. and merges of data.

////

function filterOldRevisions($tasks) {

    $revisionHash = array();

    foreach ($tasks as $taskId => $task) {
        if (isset($revisionHash[$task['noteParentId']])) {
            $currentMaxRevision = $revisionHash[$task['noteParentId']];

            if ($task['revision'] > $revisionHash[$task['noteParentId']]) {
                //store the max revision for the parent in the hash
                $previousMaxId = $revisionHash[$task['noteParentId']]['id'];
                $revisionHash[$task['parentId']]  = $task;

                //remove the previous max revision
                unset($tasks[$previousMaxId]);
            } else {
                //remove lower revision
                unset($tasks[$taskId]);
            }
        } else {
            //always store the first task
            $revisionHash[$task['noteParentId']]  = $task;
        }
    }

    return $tasks;
}

Richard · Accepted Answer · 2015-10-06 19:36:08Z

1

You can use the array_filter function http://php.net/manual/en/function.array-filter.php

example:

$parentId = 1706;
$filtered = array_filter($data, function($item) use ($parentId) { 
   return $item['noteParentId'] === $parentId; 
});

or if you modify the sql query, you can use group by and filter by count(parent_id) > 1

example:

SELECT noteParentId, count(*) FROM someTable GROUP BY noteParentId WHERE count(*) > 1;

answered Oct 6, 2015 at 19:36

Richard

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2 Comments

scrowler Over a year ago

Both of these examples are wrong. The first one will only return arrays where noteParentId is the same as what you want, and the second will only return rows where there are more than one revision.

jmchauv Over a year ago

Thank you for pointing that out Robbie. If rows have a matching noteParentId, then I want to keep the row with the highest revision out of those rows, as well as keep all of the other entries with different noteParentId's.

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