Merge keys of an array based on values

Question

I want to merge the keys of array based on values. This is my array.

Array
(
    [1] => 1
    [2] => 1
    [3] => 1
    [4] => 2
    [5] => 0
    [6] => 2
    [7] => 2
)

I want output as

Array
(
    [1,2,3] => 1
    [4,6,7] => 2
    [5] => 0
)

I have been brain storming entire day but couldn't find a solution. Any hint would be much appreciated.

WHAT I HAVE TRIED:

for($i=2;$i<=count($new);$i++){
    if ($new[$i-1][1]==$new[$i][1]){
        $same .= $new[$i-1][0].$new[$i][0];
    }
}
echo $same;

But I am stucked. I am comparing the keys one by one but it's very complicated. I don't need the code. I only need the hint or logic. Anyone kind enough?

Answer 1

<?php
$old_arr = ["1"=>1,"2"=>1,"3"=>1,"4"=>2,"5"=>0,"6"=>2,"7"=>2];
$tmp = array();
foreach($old_arr as $key=>$value)
{
  if(in_array($value, $tmp)){
      $index = array_search($value, $tmp);
      unset($tmp[$index]);
      $tmp[$index.",".$key] = $value;
  }else{
    $tmp[$key] = $value;
  }
}
ksort($tmp);
echo "<pre>";
print_r($tmp);
echo "</pre>";
?>

https://eval.in/529314