[RESOLVED] Array search for < $value

[pipe_girl]

Hello,

I need to search an array for a timestamp value that is less than another specified timestamp, returning the key for only the maximum result. I've scoured the manual but still can't figure out how to do this. Help!

[laserlight]

There are several ways, one might be:

// Let the array be $timestamps.
// Let the specified timestamp be $specified_timestamp.
$timestamps = array();
$array = array_filter($timestamps, create_function('$t', 'global $specified_timestamp; return $t < $specified_timestamp;'));
$timestamp = max($array);

It is probably more efficient to go through the array manually and check each element.

[pipe_girl]

Unfortunately what I am looking for here is the key in the original array, not the actual value, since this corresponds with a key in another array. I wanted to check to see if this is possible; otherwise I need to rethink a new approach to the whole script.

I can think of a way to do this, but it is a tad involved and I was hoping there might be a built-in function already.

[laserlight]

Unfortunately what I am looking for here is the key in the original array, not the actual value, since this corresponds with a key in another array.

Ah, rather unfortunately PHP's max() is broken in that it gives a value instead of a key.

You could do it manually:

$timestamp_key = -1;
foreach ($timestamps as $key => $value) {
    if ($value < $specified_timestamp
            && ($timestamp_key == -1 || $timestamps[$timestamp_key] < $value)) {
        $timestamp_key = $key;
    }
}
if ($timestamp_key != -1) {
    // Use the key of the maximum timestamp less than the specified timestamp.
} else {
    // There is no timestamp less than the specified timestamp.
}

[pipe_girl]

I ended up going with a while loop; when the array value exceeds the specified timestamp, -1 is subracted from the key and loop ends (it helps that the array is in a fixed ascending order). It's not pretty, but it works.

Thanks very much for your help laserlight.

[Weedpacket]

pipe_girl wrote:

It's not pretty, but it works.

Given that the array is already sorted it's likely more efficient, too. If you couldn't rely on that it would be necessary to search the entire array every time (because no matter how much of the array you've checked already, the desired value might always be in the elements you haven't checked yet). If you can stop early it's a good thing.

[pipe_girl]

Agreed.