PHP make a multidimensional associative array from key names in a string separated by brackets

Question

I have a string with a variable number of key names in brackets, example:

$str = '[key][subkey][otherkey]';

I need to make a multidimensional array that has the same keys represented in the string ($value is just a string value of no importance here):

$arr = [ 'key' => [ 'subkey' => [ 'otherkey' => $value ] ] ];

Or if you prefer this other notation:

$arr['key']['subkey']['otherkey'] = $value;

So ideally I would like to append array keys as I would do with strings, but that is not possible as far as I know. I don't think array_push() can help here. At first I thought I could use a regex to grab the values in square brackets from my string:

preg_match_all( '/\[([^\]]*)\]/', $str, $has_keys, PREG_PATTERN_ORDER );

But I would just have a non associative array without any hierarchy, that is no use to me.

So I came up with something along these lines:

$str = '[key][subkey][otherkey]';
$value = 'my_value';
$arr = [];

preg_match_all( '/\[([^\]]*)\]/', $str, $has_keys, PREG_PATTERN_ORDER );

if ( isset( $has_keys[1] ) ) {

  $keys = $has_keys[1];
  $k = count( $keys );
  if ( $k > 1 ) {
    for ( $i=0; $i<$k-1; $i++ ) {
      $arr[$keys[$i]] = walk_keys( $keys, $i+1, $value );
    } 
  } else {
    $arr[$keys[0]] = $value;
  }

  $arr = array_slice( $arr, 0, 1 );

}

var_dump($arr);

function walk_keys( $keys, $i, $value ) {
  $a = '';
  if ( isset( $keys[$i+1] ) ) {
     $a[$keys[$i]] = walk_keys( $keys, $i+1, $value );
  } else { 
     $a[$keys[$i]] = $value;
  }
  return $a;
}

Now, this "works" (also if the string has a different number of 'keys') but to me it looks ugly and overcomplicated. Is there a better way to do this?

Answer 1

I always worry when I see preg_* and such a simple pattern to work with. I would probably go with something like this if you're confident in the format of $str

<?php

// initialize variables
$str = '[key][subkey][otherkey]';
$val = 'my value';
$arr = [];

// Get the keys we want to assign
$keys = explode('][', trim($str, '[]'));

// Get a reference to where we start
$curr = &$arr;

// Loops over keys
foreach($keys as $key) {
   // get the reference for this key
   $curr = &$curr[$key];
}

// Assign the value to our last reference
$curr = $val;

// visualize the output, so we know its right
var_dump($arr);