How to sort array from file (PHP)?

First you need to build an array with an element you can actually sort on, then use usort or similar to perform the sort based on your custom criteria.

//first build up an array of databases with a unified size in bytes, ensuring
//we account for those postfixes like KB,MB,and GB
$databases=array();
while (!feof($handle)) {

    $buffer = fgets($handle, 4096);
    $data = explode(" ",$buffer);
    if (count($data)==3)
    {
        $size=$data[1];
        switch ($data[2])
        {
            case 'KB': $size*=1024; break;
            case 'MB': $size*=1024*1024; break;
            case 'GB': $size*=1024*1024*1024; break;
        }

        $data[3]=$size;
        $databases[]=$data; 
    }
    else
    {
        die("Bad line in file: $buffer");
    }
}

Now sort with a custom comparison function to sort from high to low based on that calculated size:

function cmp($a, $b)
{
    if ($a[3] == $b[3]) {
        return 0;
    }
    return ($a[3] < $b[3]) ? 1 : -1;
}

usort($databases, "cmp");

You can use the file() PHP function here.

Your text file is like :

DatabaseName 300 KB
DatabaseName 300 KB
DatabaseName 300 KB
DatabaseName 300 KB

I think you can use the PHP native function on arrays.

$data = file('myfile.txt');

foreach($data as $one_line)
{
    $db[] = explode(" ",$one_line)
    //will have $db[0][0] = 'dbname';
    //will have $db[0][2] = '30';
    //will have $db[0][2] = 'KB';   
    //will have $db[1][0] = 'dbname';
    //will have $db[1][3] = '30';
    //will have $db[1][2] = 'KB';
}
array_multisort($db[1], SORT_NUMERIC, SORT_DESC);

See this comment in documentation, the same structure : https://www.php.net/manual/en/function.array-multisort.php#79491

Or maybe you have to flip the array, so you can have size in index and name in value.

function databases_sort($a, $b) {
    if ($a[1] == $b[1]) { return 0; }
    
    return ($a[1] < $b[1]) ? -1 : 1;
}

$file_name = "test.txt";
$handle = @fopen($file_name, "r");

$databases = array();

if ($handle) { 
    while (!feof($handle)) {

        $buffer = fgets($handle, 4096);
        $data = explode(" ",$buffer);
        $databases[] = $data;
    //echo $data[1]."\n";
    }

    usort($databases, "databases_sort");
    
    foreach ($databases as $d) {
        echo $d[1];
    }

    fclose($handle);
}

This code stores your information in an array, then runs a custom sorting function on your array, sorting it by the value of element 1 in the array. Higher values (larger database sizes) get sorted to the top of the list.

Warning: I haven't actually tested this code, but you can see the usort documentation if there are any bugs that need fixing.

Edit: d'oh, beaten by a few seconds :-)

Have you thought about parsing into a binary search tree structure instead of an array? That way you could have the data sorted with a tree traversal and you could have fast lookup too.

From the very start, parse your lines into meaningful components. Calculate the bytes per database and save as a related array to the array of database lines. Use a lookup array to facilitate byte calculations. Finally, sort the db names array according to the bytes totals. Demo

$handle = fopen($file_name, "r")

$powers = ['B' => 0, 'KB' => 1, 'MB' => 2, 'GB' => 3, 'TB' => 4];
$bytes = [];
$names = [];
while (fscanf($handle, '%s %d %s', $name, $size, $unit) === 3) {
    $bytes[] = $size * 1024 ** $powers[strtoupper($unit)];
    $names[] = "$name $size $unit";
}
fclose($handle);

array_multisort($bytes, SORT_DESC, $names);
var_export($names);