PHP count # of items in an object of a given property value - php

Question

How can I count the number of items with the same folder_id# ?
Here's my list of items:
item_id=1, folder_id=1
item_id=2, folder_id=1
item_id=3, folder_id=2
item_id=4, folder_id=3
Here's my UPDATED code:
foreach($items as $item)
{
if(????) //count of $item->folder_id > 1
{
//do something to $item->folder_id=1/$item->item_id=1
}
elseif(????) // cases where $item->item_id != $item->folder_id
{
//do something else to $item->folder_id=1/$item->item_id=2
}
else
{
//do something else to $item->folder_id=2/$item->item_id=3 and folder_id=3/item_id=4
}
}
I'm interested in code that can tell me that the count for folder_id=1 is 2, the count for folder_id=2 is 1, and the count for folder_id=3 is also 1.
UPDATE: I've changed the code above to now include an elseif() because it didn't quite ask all the things I was interested in. Besides counting the # of each folder_id, I'm also interested in distinguishing cases where folder_id != item_id. This would put item_id=1, item_id=2, item_id=3/4 in their own conditional clauses and wouldn't lump item_id=1 and item_id=2 as before.
Any assistance would be greatly appreciated, thank you,

Answer 1

If you had an array of folder_ids, you could use array_count_values to provide exactly the result you need. So let's make an array like that out of an array of objects using array_map:
$callback = function($item) { return $item->folder_id; };
$result = array_count_values(array_map($callback, $items));
This will end up with $result being
array(
1 => 2,
2 => 1,
3 => 1,
);
You can also write the callback inline for an one-liner, or if you are on PHP < 5.3 you can write it as a free function or alternatively using create_function.
See it in action (version for PHP < 5.3).
Update: follow up
Given $results from above, your loop would be:
foreach($results as $folder_id => $count) {
if($count > 1) {
// There were $count items with folder_id == $folder_id
}
// else blah blah
}

Answer 2

$totals = array();
foreach($items as $item) {
$totals[$item->folder_id]++;
}

Answer 3

function count_items(Array $items, $folder_id) {
return count(array_filter($items,
function($item) use($folder_id) {
return $item->folder_id === $folder_id;
}
));
}

Answer 4

I think this is what you are looking for.
function folder_count($items, $num)
{
$cnt = 0;
foreach($items as $item)
{
if($item->folder_id > $num)
{
$cnt++;
}
}
return $cnt;
}
foreach ($items as $item)
{
if (folder_count($items, 1))
{
//do something to $item->folder_id=1/$item->item_id=1, item_id=2
}
else
{
//do something else to $item->folder_id=2/$item->item_id=3 and folder_id=3/item_id=4
}
}