How to “flatten” a multi-dimensional array to simple one in PHP?

Question

It\'s probably beginner question but I\'m going through documentation for longer time already and I can\'t find any solution. I thought I could use implode for each dimensio

Answer 1

Sorry for necrobumping, but none of the provided answers did what I intuitively understood as "flattening a multidimensional array". Namely this case:

[
  'a' => [
    'b' => 'value',
  ]
]

all of the provided solutions would flatten it into just ['value'], but that loses information about the key and the depth, plus if you have another 'b' key somewhere else, it will overwrite them.

I wanted to get a result like this:

[
  'a_b' => 'value',
]

array_walk_recursive doesn't pass the information about the key it's currently recursing, so I did it with just plain recursion:

function flatten($array, $prefix = '') {
    $return = [];
    foreach ($array as $key => $value) {
        if (is_array($value)) {
            $return = array_merge($return, flatten($value, $prefix . $key . '_'));
        } else {
            $return[$prefix . $key] = $value;
        }
    }
    return $return;
}

Modify the $prefix and '_' separator to your liking.

Playground here: https://3v4l.org/0B8hf