JuniorTheoryCommon

What does the program print?

PHP

<?php

$nums = [5, 8, 1, 6];
$even = array_filter($nums, fn($n) => $n % 2 === 0);
echo json_encode($even), ' ', json_encode(array_values($even)), "\n";

{"1":8,"3":6} [8,6]

Expecting array_filter to renumber the values it keeps: it keeps their original keys, so the even numbers of [5, 8, 1, 6] sit under keys 1 and 3 and json_encode writes an object.
Expecting the function to pick what to drop: array_filter keeps every value for which the function returns true and drops the rest.

What does array_filter keep when you call it without a function?
Why can a frontend receive a JSON object instead of an array after a filter?

Back to questions Open topic in roadmap →Answer it yourself — Quiz

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JuniorTheoryCommon

What does the program print?

PHP

<?php

$nums = [5, 8, 1, 6];
$even = array_filter($nums, fn($n) => $n % 2 === 0);
echo json_encode($even), ' ', json_encode(array_values($even)), "\n";

{"1":8,"3":6} [8,6]

Expecting array_filter to renumber the values it keeps: it keeps their original keys, so the even numbers of [5, 8, 1, 6] sit under keys 1 and 3 and json_encode writes an object.
Expecting the function to pick what to drop: array_filter keeps every value for which the function returns true and drops the rest.

What does array_filter keep when you call it without a function?
Why can a frontend receive a JSON object instead of an array after a filter?

Back to questions Open topic in roadmap →Answer it yourself — Quiz