PHP array_keys - what am I doing wrong?

I have two arrays:

$fieldNames:

array(
[0] => array(
    ['fieldName'] =>'id'
    ['fieldType'] => 'int(11)'
    )
[1] =>
    ['fieldName'] =>'adminID'
    ['fieldType'] =>'int(11)'
    )
[2] =>array(
    ['fieldName'] =>'schoolID'
    ['fieldType'] =>'int(11)'
    )
[3] => array(
    ['fieldName'] =>'lessonPlanName'
    ['fieldType'] =>'varchar(255)'
    )
[4] =>array(
    ['fieldName'] =>'lessonPlanAssignmentDate'
    ['fieldType'] =开发者_开发问答>'varchar(255)'
    )
[5] =>array(
   ['fieldName'] =>'lessonPlanDueDate'
   ['fieldType'] =>'varchar(255)'
   )
[6] =>array(
   ['fieldName'] =>'lessonPlanTopics'
   ['fieldType'] =>'varchar(255)'
   )
[7] =>array(
   ['fieldName'] =>'lessonPlanDescription'
   ['fieldType'] =>'text'
   )
[8] =>array(
   ['fieldName'] =>'lessonPlanNotes'
   ['fieldType'] =>'text'
   )
)

$formElementPairs:

array(
   ['lessonPlanName'] =>'Test'
   ['lessonPlanAssignedDate'] =>'05/11/2011'
   ['lessonPlanDueDate'] =>'05/11/2011'
   ['lessonPlanTopics'] => 1
   ['lessonPlanDescription'] =>'test'

)

I'm trying to check to see if array 2 is missing any of the 'fieldName' keys from array 1 and then add them to array 2 with null entries. The following code works in that I am getting the "fieldName" values from the first array (id, adminId, schoolId, etc.) but when I go to check them against the second array using array_keys, my resulting array always has a count of 0. Should also mention I am stuck using PHP4 on this project.

//merge arrays
for($fn=0; $fn<count($fieldNames); $fn++) { 
    $thisFieldName = $fieldNames[$fn]['fieldName'];
    $fieldCheckArray = array_keys($formElementPairs, $thisFieldName);
    //$firephp->fb(count($fieldCheckArray));
}

Am I misunderstanding array_keys and/or is there a more elegant way to do this in PHP4?

Thanks

You can use the array_key_exists to check if array 2 is missing anything: array_key_exists

$missing = array();
for($fn=0; $fn<count($fieldNames); $fn++) { 
    $thisFieldName = $fieldNames[$fn]['fieldName'];
    if(!array_key_exists($thisFieldName, $formElementPairs)) {
        $missing[] = $thisFieldName;
    }
}
//do something with $missing

The second argument to array_keys is attempting to match the values and not the keys of $formElementPairs.