Php versions - Which PHP function returns a smaller version of my associative array containing only keys present as values in a second array?

ElectricGecko
June 17, 2023
231 views
0 votes
2 Answers

The PHP function that I’m looking for is similar to array_intersect_key().

If I have an associative array called $populations[], and a numerical array called $countries[], which function will return a modified version of $populations[] with only keys present as values in $countries?

Here’s a pair of arrays that I may want such a function for:

$populations = [
    'Sweden' => 6476727,
    'Denmark' => 3722898,
    'Finland' => 3417691,
    'Norway' => 3511912,
    'Iceland' => 247524
];

$countries = [
    'Sweden',
    'Denmark',
    'Norway'
];

Which function will take those two arrays as input, and output the following array?

['Sweden']=> 6476727
['Denmark']=> 3722898
['Norway']=> 3511912

Tags: function php

Answers

- Barmar
- June 16, 2023 at 10:56 pm
- 0 votes
0
I don’t think there’s a single function that does it. But you can flip $countries into an associative array and then use array_intersect_key().
```
$result = array_intersect_key($populations, array_flip($countries));
```
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- ArleighHix
- June 16, 2023 at 11:36 pm
- 0 votes
0
Try out array_filter, you pass a simple custom callback closure that returns true if the item is to be included in the resulting array, in this case :in_array($key, $countries).
```
$populations = [
    'Sweden' => 6476727,
    'Denmark' => 3722898,
    'Finland' => 3417691,
    'Norway' => 3511912,
    'Iceland' => 247524
];

$countries = [
    'Sweden',
    'Denmark',
    'Norway'
];

$filtered = array_filter($populations, function($key) use ($countries) {
    return in_array($key, $countries);
}, ARRAY_FILTER_USE_KEY);

var_export($filtered);
/*
array (
  'Sweden' => 6476727,
  'Denmark' => 3722898,
  'Norway' => 3511912,
)
*/
```
Also, see PHP function use variable from outside

Note:

This will be less performant than Barmar’s answer, but will be easier to understand when you revisit the code weeks, months, or years later.
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