How can I stuff the results of this for loop into an array?

Here's my array:

$my_array=array ( 
	0 => array ( 'id' => '1', 'column_name' => 'screeningsubperiod', 'column_data' => 'screeningsubperiod_data', ), 
	1 => array ( 'id' => '2', 'column_name' => 'screeningperiodid', 'column_data' => 'screeningperiodid_data', ), 
	2 => array ( 'id' => '3', 'column_name' => 'screeningtime', 'column_data' => 'screeningtime_data', ), 
	3 => array ( 'id' => '4', 'column_name' => 'bfull', 'column_data' => 'bfull_data', ), 
);

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When I run this code...

<?php
$num=count($my_array);
$numberfields=count($my_array[0]);

$i=0;
foreach($my_array as $row)
{
	
	foreach($row as $key=>$value)
	{		
		$fieldname="";
		$fieldvalue="";
		$fieldname=$key;
		$fieldvalue=$value;
		
		//$data[$fieldname] = $fieldvalue;
		$data[$i][$fieldname]=[$fieldvalue];
		$i++;
	}
}
var_dump($data);


?>

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...I get this:


I need to "dig" into the array like this:

if($data['column_name']=="screeningsubperiod")
{
echo "yes";
}

I keep getting an error that says I'm using an undefined index and I understand WHY I'm getting that error, I just don't know how to build my array in a manner that allows me to check specific values.

Ideally, I need the array to look like this:

0 => array ( 'id' => '1', 'column_name' => 'screeningsubperiod', 'column_data' => 'screeningsubperiod_data', ),

Right now, I'm getting a separate array for every column heading. How can I fix that and then how can I drill down into that array and check for specific values?
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