How to combine multiple arrays of duplicate first element (Combine only second element) in PHP?

I've an array of arrays in which I've 2 values in each array first one is personID and second one is Skill, there are multiple skills of same persons I need all same skills to add in an array with single person id. I can't figure how to do it.

Raw Data With Duplicate IDs

$data = array(
    array(1, "Writing"),
    array(3, "Designing"),
    array(1, "Problem Solving"),
    array(3, "Communication"),
    array(5, "Writing"),
    array(5, "Planning and organising"),
    array(5, "Communication"),
    array(1, "Designing"),
    array(2, "Leadership"),
    array(2, "Communication"),
    array(2, "Designing")
);

Need Data Format With Unique Person IDs

$data = array(
    array(1, "Writing", "Problem Solving", "Designing"),
    array(3, "Designing", "Communication"),
    array(5, "Writing", "Planning and organising", "Communication"),
    array(2, "Leadership", "Communication", "Designing")
)

You can loop through the input array $data and build a new array - in this case $dataCombined - with the combined second values:

<?php
$firstValues = array();  // array of first values
$dataCombined = array();   // new array with the combined data

// loop through array $data
for($i=0;$i<count($data);$i++)
{
// first value
$firstValue = array_values($data[$i])[0];
// second value
$secondValue = array_values($data[$i])[1];

  // write first values in array $firstValues if missing and fill new array $dataCombined
  if(!in_array($firstValue,$firstValues))
  {
  $firstValues[] = $firstValue ;
  $dataCombined[] = array($firstValue, $secondValue);
  }
  else
  {
    // if first values match combine second values in a new loop
    for($j=0;$j<count($dataCombined);$j++)
    {
    $duplicateFirstValue = array_values($dataCombined[$j])[0];
    $otherSecondValue = array_values($dataCombined[$j])[1]; 
    // case first values match
    if($firstValue === $duplicateFirstValue)
    {
    // fill new array with combined second data
    $dataCombined[$j][1] = $otherSecondValue.",".$secondValue;
    }
    }
  }
}
print_r($dataCombined);
?>