transform a two-dimensional array into a table-like structure

Question

I have as input a 2 dimensional array. Example:

$input = [
  [1,2,3], 
  [11, "a" => "val_a"],
  [12,'b' => 'val_b', 'a' => 'val2_a'],
  [2 => 22]
];

I want to convert it to an array with a tabular structure. In the table-like structure, all sub-arrays (rows) have exactly the same key in the same order. These keys are the union of all keys of the 2nd level.

New Keys: [0, 1, 2, 'a', 'b']

Elements that do not exist in the input array receive the value NULL. I expect the following result:

$expected = [
  [ 0 => 1,  1 => 2,    2 => 3,    'a' => NULL, 'b' => NULL],
  [ 0 => 11, 1 => NULL, 2 => NULL, 'a' => "val_a", 'b' => NULL],
  [ 0 => 12, 1 => NULL, 2 => NULL, 'a' => "val2_a", 'b' => "val_b"],
  [ 0 => NULL, 1 => NULL, 2 => 22, 'a' => NULL, 'b' => NULL]
];

What I've tried so far:

function rectify($array){
    $maxRow = [];
    foreach($array as $row){
      $maxRow += $row;
    }
    $new = [];
    foreach($array as $key => $row){
      foreach($maxRow as $mKey => $mVal){
        $new[$key][$mKey] =  array_key_exists($mKey,$row) ? $row[$mKey] : NULL;
      }
    }
    return $new;
  }

The function delivers correct results. The solution is very complex due to 2 nested loops with one query. Another attempt returned the same keys, but not in the same order.

Side note: if you're looking for improvement for a working algorithm, Code review might be a better place. — El_Vanja
– El_Vanja, Commented Apr 9, 2021 at 16:57

Nigel Ren · Accepted Answer · 2021-04-09 17:03:03Z

2

This code first identifies all of the columns in the data. It then creates an empty template array (using array_unique to remove duplicates).

It then loops over the rows again and uses array_replace to fill the values in for each row...

$headers = [];
foreach ( $input as $row )  {
    $headers = array_merge($headers, array_keys($row));
}
$headers = array_fill_keys(array_unique($headers), null);
$output = [];
foreach ( $input as $row )  {
    $output[] = array_replace($headers, $row);
}

answered Apr 9, 2021 at 17:03

Nigel Ren

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1 Comment

jspit Over a year ago

array_replace is a good idea. Many Thanks.

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