How do I detect groups of common strings in filenames

Question

I'm trying to figure out a way to detect groups of files. For instance:

If a given directory has the following files:

• Birthday001.jpg
• Birthday002.jpg
• Birthday003.jpg
• Picknic1.jpg
• Picknic2.jpg
• Afternoon.jpg.

I would like to condense the listing to something like

• Birthday ( 3 pictures )
• Picknic ( 2 pictures )
• Afternoon ( 1 picture )

How should I go about detecting the groups?

Answer 1

Here's one way you can solve this, which is more efficient than a brute force method.

• load all the names into an associative array with key equal to the name and value equal to the name but with digits stripped (preg_replace('/\d//g', $key)).

You will have something like $arr1 = [Birthday001 => Birthday, Birthday002 => Birthday ...]

• now make another associative array with keys that are values from the first array and value which is a count. Increment the count when you've already seen the key.
• in the end you will end up with a 2nd array that contains the names and counts, just like you wanted. Something like $arr2 = [Birthday => 2, ...]

Answer 2

Simply build a histogram whose keys are modified by a regex:

<?php

# input
$filenames = array("Birthday001.jpg", "Birthday002.jpg", "Birthday003.jpg", "Picknic1.jpg", "Picknic2.jpg", "Afternoon.jpg");

# create histogram
$histogram = array();
foreach ($filenames as $filename) {
    $name = preg_replace('/\d+\.[^.]*$/', '', $filename);
    if (isset($histogram[$name])) {
        $histogram[$name]++;
    } else {
        $histogram[$name] = 1;
    }
}

# output
foreach ($histogram as $name => $count) {
    if ($count == 1) {
        echo "$name ($count picture)\n";
    } else {
        echo "$name ($count pictures)\n";
    }
}

?>