Removing Keys In Associative Array Not Working - php

Question

I am trying to retain only certain keys, and remove the rest from an external API. I have an array (http://pastebin.com/vU8T4y7h), "data" containing the objects:
foreach ($data as $media) {
foreach (array_keys($media) as $media_key) {
if ($media_key!=="created_time" && $media_key!=="likes" && $media_key!=="images" && $media_key!=="id") {
unset($media[$media_key]);
}
}
}
In this case, I am trying to only keep the created_time, likes, images, and id keys, however, the above code isn't working. Any ideas as to why? Any other elegant solutions to achieve the same thing?

Answer 1

The reason this isn't working is because you aren't unsetting from the original $data object. You can fix it one of two ways. Either access by reference or update your unset to act on the original $data object instead.
Using reference:
foreach($data as &$media) {
Unsetting from $data
unset($data[$media][$media_key]);

Answer 2

foreach creates a copy of each array element, so unsetting $media[$media_key] only unsets from the copy; and you want to unset from the original $data array:
foreach ($data as $mediaRef => $media) {
foreach (array_keys($media) as $media_key) {
if ($media_key!=="created_time" && $media_key!=="likes" && $media_key!=="images" && $media_key!=="id") {
unset($data[$mediaRef][$media_key]);
}
}
}
or (by reference)
foreach ($data as &$media) {
foreach (array_keys($media) as $media_key) {
if ($media_key!=="created_time" && $media_key!=="likes" && $media_key!=="images" && $media_key!=="id") {
unset($media[$media_key]);
}
}
}
unset($media);

Answer 3

Asking for an elegant solution:
foreach ($data as $key => $media) {
foreach (array_keys($media) as $media_key) {
if (!in_array($media_key, array("created_time", "likes", "images", "id"))) {
unset($data[$key][$media_key]);
}
}
}
I'd try to avoid using references in foreach loops because you need to unset the referenced variable. If not, hard to detect errors occur.

Answer 4

You can use array_intersect_key to do that kind of thing easily:
$keepTheseKeys = array_flip(array('created_time', 'likes', 'images', 'id'));
foreach ($data as &$media) {
$media = array_intersect_key($media, $keepTheseKeys);
}
unset($media);
The error
The error in the code in the question is that you're updating a temporary variable, either pass media by reference (see above example) - or refer to the original variable:
foreach ($data as $i => $media) {
$data[$i] = ...

Answer 5

First, you don't need to use
foreach (array_keys($media) as $media_key) {
you can use
foreach($media as $media_key => $media_value){
instead
But for your question, in the first line, you are going through $data, and in each cycle, the current value in $data is assigned into $media. But media doesn't have any connection back to original $data, so it is discarded on next iteration, when new value is assigned from $data to $media.
You have two options:
Use references:
foreach($data as &$media) { // and so on... this should work, but i don't suggest it
in first line, write
foreach($data as $media_k => $media) {
and in fourth line, write
unset($data[$media_k][$media_key]); //