php array values compare

Question

Hi people I need your help. Let's say I have an array.

$arr = array(
1  => array(
       key1 => something,
       key2 => something,
       key3 => something,          
       testkey => 3,           
       keyx...),
2  => array(
       key1 => something,
       key2 => something,
       key3 => something,          
       testkey => 0,           
       keyx...),
3  => array(
       key1 => something,
       key2 => something,
       key3 => something,          
       testkey => 2,           
       keyx...),
4  => array(
       key1 => something,
       key2 => something,
       key3 => something,          
       testkey => 2,           
       keyx...),
5  => array(
       key1 => something,
       key2 => something,
       key3 => something,          
       testkey => 3,           
       keyx...),
6  => array(
       key1 => something,
       key2 => something,
       key3 => something,          
       testkey => 0,
       keyx),
7  => array(
       key1 => something,
       key2 => something,
       key3 => something,          
       testkey => 3,           
       keyx...),
n =>array(blabla)
)

I can't know how many keys $arr has.

I need to test if one or more value of testkey are equal, if they are put this result on a variable.

2 and 6 are not considered since the testkey is 0.

(0 is my default value, i can put it to NULL)

3 and 4 have the value of 1 (first to match).

1, 5 and 7 have the value of 2 (second to match).

Then I have to store this values somehow:

$matched = array();
    $matched[1] = array (2, 6);
    $matched[2] = array (1, 5, 7);

But I'm sure it can be done better.

Thank you.

Answer 1

I would sort the array $arr by the testkey values. This can be done in O(n lg n) time. Then you iterate through the sorted array and adds the original keys to $matched[1] . When the testkey value changes, you start adding the next key values to $matched[2] , etc.