PHP Get the value of every occurrence of a key in a multidimensional array

September 20, 2023

How would you extract every value of a key regardless of how deep or shallow it is in an array.

Here is a sample JSON array. I want to grab every occurrence of "content" and concatenate them into a single string.

{
  "foo": [
    "content": "hi",
    "inner": []
  ],
  "bar": [
    "content": "hi2",
    "inner": [
      {
        "bat": [
          "content": "hi3",
          "inner": []
        ],
      }
    ]
  ]
}

Theoretically that could go on for ever with inner of inner of inner. How do we grab all the content values?

>Solution :

I would use array_walk_recursive() for this, as it is pretty straightforward.

//convert JSON to an array
$data = json_decode($json_data, true);

//create an empty array to hold all of the values we are collecting
$content_values = [];

//this `function` is called for every key in the array that does not contain another array as it's value
//We also pass $content_values as a reference, so we can modify it inside the function
array_walk_recursive($data, function ($value, $key) use (&$content_values) {
    if ($key === 'content') {
        $content_values[] = $value;
    }
});

//Lastly, implode all of the array elements into a string with the given separator
$concatenated_content = implode(', ', $content_values);
echo $concatenated_content;

Output