<?php
$files = glob('*.txt');
$stack = array();
foreach ($files as $file) {
        $content = substr(file_get_contents($file), 0, -1);
        $students = array_unique(explode('|', $content));
        foreach ($students as $student) {
                if (empty($student) === true) {
                        continue;
                }
                if (array_key_exists($student, $stack) === false) {
                        $stack[$student] = 1;
                } else {
                        $stack[$student] = $stack[$student] + 1;
                }
        }
}
asort($stack);

foreach ($stack as $k => $v) {
        echo sprintf('%s était là durant %d séances'."\n", $k, $v);
}