<?php
$arrayOld = array(
    '17' => array('1'),
    '11' => array('2'),
    '10' => array('6'),
    '9' => array('1'),
);
$arrayNew = [];

foreach($arrayOld as $key => $value){
    $arrayNew[] = [(string)$key,$value[0]];
}

var_export ($arrayNew);

$old = array(
    '17' => '1',
    '11' => '2',
    '10' => '6',
    '9' => 1 
);

$new = array_chunk($old, 1, true);
foreach ($new as $key => &$val) {
    array_unshift($val, $key);
}
var_dump($new);

<?php

  $data= array(
    '17' => array('1'),
    '11' => array('2'),
    '10' => array('6'),
    '9' => array('1'),
  );

  function maps(&$array,$key) {
    array_unshift($array, $key);
  }

  array_walk($data, 'maps');
  print_r($data);
?>

The answers given by the respondents above are all quite good, and I can’t help but express my ugliness

$old = [
  '17' => ['1'],
  '11' => ['2'],
  '10' => ['6'],
  '9' => ['1'],
];
$new = [];
foreach ($old as $key => $value) {
  $new[] = [$key, $value[0]];
}
var_dump($new);

It’s actually quite simple. The answer won’t be much different, so I’ll simply add some explanations

First of all, you need to learn to traverse foreach, and then PHP is a weakly typed language, and the variable type is converted by itself

Oh yes, the other thing you need to know is $arr[] = $var, which is like adding elements to the end of an array. Another method is array_push($arr, $var), but this method is less efficient than the first one