Efficiently find nested PHP array element based on attribute value

Question

Suppose a PHP array, when cast to JSON, has the following format:

[{
    "key": "width",
    "value": "1200",
    "label": "Width (mm)",
    "choice": ""
},
{
    "key": "height",
    "value": "900",
    "label": "Height (mm)",
    "choice": ""
},
{
    "key": "material",
    "value": "paper",
    "label": "Material",
    "choice": "Paper"
}]

(This is a shortened version of the original, which can have many more elements)

Let's suppose I want to efficiently find what material is used. In other words, I want to search for a nested array that has for key the value material, and I want to return the value which would be paper.

I know this can be done by using a foreach/while loop, but PHP is rich with compiled array functions that I'm not very familiar with. What's the best function to use here?

UPDATE: What I've tried so far

Here's two things I've tried so far:

Attempt #1:

$json = '[{"key":"width","value":"1200","label":"Width (mm)","choice":""},{"key":"height","value":"900","label":"Height (mm)","choice":""},{"key":"material","value":"paper","label":"Material","choice":"Paper"}]';
$array = json_encode($json, true);
$material = '';
foreach($array as $nestedArray) {
  if($nestedArray['key'] = 'material') {
    $material = $nestedArray['value'];
  }
}

Attempt #2:

$json = '[{"key":"width","value":"1200","label":"Width (mm)","choice":""},{"key":"height","value":"900","label":"Height (mm)","choice":""},{"key":"material","value":"paper","label":"Material","choice":"Paper"}]';
$array = json_decode($json, true);
$filteredArray = array_filter($array, function($array) {
    return ($array['key'] == 'material');
});
$arr = array_pop($filteredArray)['value'];

Both produce the right value, but #1 is messy, and #2 may not be the best use of PHPs array functions.

Efficient as in microoptimize, or efficient as in memory usage, or efficient as in code written? — mario
– mario, Commented Sep 21, 2017 at 6:29
@Andreas it originally exists as a JSON text string, correct — e_i_pi
– e_i_pi, Commented Sep 21, 2017 at 6:33
@mario, efficient as in not loop through 100 nested arrays looking at each one, and instead using a function like array_filter(), which doesn't quite fit the bill — e_i_pi
– e_i_pi, Commented Sep 21, 2017 at 6:33

Jigar Shah · Accepted Answer · 2017-09-21 07:14:55Z

2

It depends on what you want to do in addition to "finding the value". And what you have.

array_filter is simple, but it will loop through the whole array.

array_search on a reduced set looks faster, but it needs to make a copy of the source array, so it's actually slower than array_filter (not by much).

The foreach solution you tried first will not create extra arrays and it allows you to break on a find:

foreach($array as $nestedArray) {
    if ($nestedArray['key'] == 'material') {
        $material = $nestedArray['value'];
        break; // <--- found!
    }
}

So on short arrays I'd go with the accepted solution using array_column, or if you're sure that the material is there, there is this array_column tweak:

// Transform the records into keypairs
$keypairs = array_column($records, 'value', 'key');

Now keypairs is [ width => 900, material => paper, ... ], so:

$material = $keypairs['material'];

I'd add a array_key_exists just to be sure. This saves the array_search (not that great an advantage, but you might have a use for the keypair object).

If you need exactly that one value and nothing else, performance is at a premium, and the array is large, I'd not throw out the idea of looking for '"material":"' inside the JSON as a string with strpos, even if it's a code smell.

edited Sep 21, 2017 at 7:14

Jigar Shah

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answered Sep 21, 2017 at 6:56

LSerni

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1 Comment

e_i_pi Over a year ago

Across 10000 iterations, this function is more efficient, and returning the keypairs could come in handy. I'm changing the accepted answer to this one, thanks @LSemi

Andreas · Accepted Answer · 2017-09-21 06:38:07Z

1

If it's a json text as you stated in comments my advice is a regex match.

This will find "key material" and "value" and match the value of value.
It works on the small sample, but you have to try it on a larger string.

https://regex101.com/r/CSTLUL/1

$re = '/key\": \"material\",.*?\"value\": \"(.*?)\",/s';
$str = '{
"key": "width",
"value": "1200",
"label": "Width (mm)",
"choice": ""
},
{
"key": "height",
"value": "900",
"label": "Height (mm)",
"choice": ""
},
{
"key": "material",
"value": "paper",
"label": "Material",
"choice": "Paper"
}]';

preg_match_all($re, $str, $matches);

// Print the entire match result
var_dump($matches);

answered Sep 21, 2017 at 6:38

Andreas

24k7 gold badges34 silver badges75 bronze badges

2 Comments

e_i_pi Over a year ago

Thanks for the answer @Andreas, but I prefer Jigar's answer which uses the PHP array functions

Andreas Over a year ago

Sure. No problem.

Community · Accepted Answer · 2023-11-17 20:33:26Z

1

You can use combination of array_search and array_column so no need to use loop

Working Demo: https://eval.in/865566

$data = '[{
    "key": "width",
    "value": "1200",
    "label": "Width (mm)",
    "choice": ""
},
{
    "key": "height",
    "value": "900",
    "label": "Height (mm)",
    "choice": ""
},
{
    "key": "material",
    "value": "paper",
    "label": "Material",
    "choice": "Paper"
}]';
$data = json_decode($data,True);


$key = array_search('material', array_column($data, 'key')); // get key of array
echo $data[$key]['value'];

Output

paper

edited Nov 17, 2023 at 20:33

CommunityBot

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answered Sep 21, 2017 at 6:38

Jigar Shah

6,2332 gold badges32 silver badges41 bronze badges

2 Comments

e_i_pi Over a year ago

Brilliant, exactly the sort of thing I was looking for. I'd just stumbled upon the array_search/array_column trick, but was having trouble getting it working properly.

Jigar Shah Over a year ago

Thanks, glad to help you :)

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