Question

Currently I’m using foreach to search key when use array_replace:

$grades = array(
               0 =>array('id'=>1, 'grade'=>4),
               1 =>array('id'=>5, 'grade'=>2), 
               2 =>array('id'=>17,'grade'=>1),
             )
$replacement = array('id'=>17,'grade'=>3);

foreach($grades as $key=>$grade){
    if($grade->id ==$replacement['id'] )
       $found = $key;
}
$new_grades = array_replace($grades, array($found_key=>$replacement));

I wonder if this will become inefficient when the number of elements grow too much in $grades array. Is there any better way to do the search and replace job?

Answer 1

The execution time grows linearly with the number of elements in the array (O(N)). Use a better data structure, i.e. use the array in an associative way with the ID as index:

$grades = array(
    1 => array('grade'=>4),
    5 => array('grade'=>2), 
    17 => array('grade'=>1)
);

Then the lookup cost is constant (O(1)). You can do:

$grades[$replacement['id']] = array('grade' => $replacement['grade']);

or something similar, depending on your data.