Sorry to bump this, but I'm really hoping someone can help me understand
this.
-Walter
On Monday, September 14, 2015 at 10:08:55 AM UTC+2, Walter Vos wrote:
>
> Hi!
>
> I'm having trouble wrapping my head around Collection::reduce. Actually,
> it feels like I understand how it's supposed to work, but in reality it
> seems to work differently. I have a collection of entities, from which I'm
> trying to concat a number of string, based on another array (could probably
> also be an array, I don't think it would matter much). The array has an ID,
> the collection has that ID as a foreign ID. I loop through the array, and
> then in each loop I loop through the collection to find the entities which
> have a foreign ID matching the ID from the array. Implementing this with
> Collection::reduce gives a wildly different result from doing it with two
> foreach() loops. Anyway, here's the code:
>
> public function reducetest() {
> $this->render('test');
>
> $groupby = ['a' => 1, 'b' => 2];
> $array = [
> array('id' => 'b', 'title' => 'array_tag_1'),
> array('id' => 'a', 'title' => 'array_tag_2'),
> array('id' => 'b', 'title' => 'array_tag_3'),
> array('id' => 'a', 'title' => 'array_tag_4'),
> array('id' => 'a', 'title' => 'array_tag_5')
> ];
> $array_result = array();
> foreach ($groupby as $key => $value) {
> $array_result[$key] = '';
> foreach ($array as $item) {
> if ($key === $item['id']) {
> // debug($array_result[$key] . $item['title'] . ", \n");
> $array_result[$key] .= $item['title'] . ', ';
> }
> }
> $array_result[$key] = trim($array_result[$key], ', ');
> }
> debug($array_result);
>
> $collection = new Collection([
> array('id' => 'b', 'title' => 'collection_tag_1'),
> array('id' => 'a', 'title' => 'collection_tag_2'),
> array('id' => 'b', 'title' => 'collection_tag_3'),
> array('id' => 'a', 'title' => 'collection_tag_4'),
> array('id' => 'a', 'title' => 'collection_tag_5')]
> );
> $collection_result = array();
> foreach ($groupby as $key => $value) {
> $collection_result[$key] = $collection->reduce(function ($string,
> $item) use ($key) {
> if ($key === $item['id']) {
> // debug($string . $item['title'] . ", \n");
> return $string . $item['title'] . ', ';
> }
> }, '');
> $collection_result[$key] = trim($collection_result[$key], ', ');
> }
> debug($collection_result);
> }
>
> The code with the two foreach() loops produces this result, as expected:
>
> [
> 'a' => 'array_tag_2, array_tag_4, array_tag_5',
> 'b' => 'array_tag_1, array_tag_3'
> ]
>
> The code that uses the reduce function gives this result, incomprehensibly
> to me:
>
> [
> 'a' => 'collection_tag_4, collection_tag_5',
> 'b' => ''
> ]
>
> Who can explain to me what I'm not understanding here?
>
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