How to classify array items? - php

Question

I have a query which fetches all comments for question and answers in one page (each page is containing at least one post (question), and maybe plus one or more posts (answers)). Now I need to separate comments according to its own question or answers.
The result of my query (fetching all comments) is something like this:
while ($results = $sth->fetch(PDO::FETCH_ASSOC)) {
echo '<pre>';
print_r($results);
}
/* Output:
Array
(
[id] => 1
[post_id] => 1
[content] => Have you any tried so far?
)
Array
(
[id] => 2
[post_id] => 3
[content] => Great answer, upvote
)
Array
(
[id] => 3
[post_id] => 3
[content] => That semicolon is redundant in line 5. Pplease edit it
)
Array
(
[id] => 4
[post_id] => 2
[content] => Won't work ...!
)
Array
(
[id] => 5
[post_id] => 3
[content] => #alex You are right thanks, Edited.
)
So, as you see in the output, all comments are mixed.. Now I need to classify them. Something like this:
/* NewOutput:
[1] => Array
post_id ^ (
[0] => Array
(
[id] => 1
[content] => Have you any tried so far?
)
)
[2] => Array
post_id ^ (
[0] => Array
(
[id] => 4
[content] => Won't work ...!
)
)
[3] => Array
post_id ^ (
[0] => Array
(
[id] => 2
[content] => Great answer, upvote
)
[1] => Array
(
[id] => 3
[content] => That semicolon is redundant in line 5. Pplease edit it
)
[2] => Array
(
[id] => 5
[content] => #alex You are right thanks, Edited.
)
)
Well, Now I want to know, how can I create a nested array according to the value of specific key in the array? exactly like above.

Answer 1

Try this...
$output = array();
foreach($results as $r){
$key = "post_".$r["post_id"];
if(!array_key_exists($key, $output)){
$output[$key] = array();
}
array_push($output[$key], array("id"=>$k["id"], "content"=>$k["content"]));
}
print_r($output);