different results array shortcode PHP [closed] - php

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I have a question about the differents between the normal array code and the shortcode.
The output from the shortcode version has all the results.
But the normal code has only the last record of the data from the database.
Please is there somebody who can explain this?
Below the shortcode
<?php
while ($data = mysqli_fetch_assoc($result)) {
$output[$data['category']][] = $data['type'];
}
?>
Below the normal code
<?php
while ($data = mysqli_fetch_assoc($result)) {
//alleen laatste database result
$output = array($data['category'] => array($data['type']));
}
?>

Answer 1

When you assign
$output = <anything>;
you discard all the previous contents of $output, and replace it with the value of <anything>. So each time through the loop in the second version, you replace the variable with the data from the current row. When the loop is done, it just has the data from the last row.
You don't want to replace all of $output. It should be a multi-dimensional array, where the first dimension is associative with categories as keys, and the second dimension is an array of all type values in that category. Assigning to
$output[$data['category']][]
does two things:
$output[$data['category']] creates the category key in the first dimension if it doesn't already exist.
Assigning to [] pushes a new element onto the array in the second dimension.
It's equivalent to the following long code
while ($data = mysqli_fetch_assoc($result)) {
$cat = $data['category'];
if (!isset($output[$cat])) {
$output[$cat] = array();
}
array_push($output[$cat], $data['type']);
}