Q:

PHP group certain results from foreach on array into another array

I have an array that looks something like this:
$array =  array( [0] => FILE-F01-E1-S01.pdf 
                 [1] => FILE-F01-E1-S02.pdf 
                 [2] => FILE-F01-E1-S03.pdf 
                 [3] => FILE-F01-E1-S04.pdf 
                 [4] => FILE-F01-E1-S05.pdf 
                 [5] => FILE-F02-E1-S01.pdf 
                 [6] => FILE-F02-E1-S02.pdf 
                 [7] => FILE-F02-E1-S03.pdf );

Basically, I need to look at the first file and then get all the other files that have the same beginning ('FILE-F01-E1', for example) and put them into an array. I don't need to do anything with the other ones at this point.
I've been trying to use a foreach loop finding the previous value to do this, but am not having any luck.
Like this:
$previousFile = null;

foreach($array as $file)
{

    if(substr_replace($previousFile, "", -8) == substr_replace($file, "", -8)) 
    {
        $secondArray[] = $file;
     }

    $previousFile = $file;
}

So then $secondArray would look like this:
    Array ( [0] => FILE-F01-E1-S01.pdf [1] => FILE-F01-E1-S02.pdf 
            [2] => FILE-F01-E1-S03.pdf [3] => FILE-F01-E1-S04.pdf 
            [4] => FILE-F01-E1-S05.pdf)

As my result.
Thank you!

A:

Are you sure this will be the naming format? That is crucial information to have to construct a regexp or something to check for being a substring of the following strings.
If we can assume this and that the "base" name is always at index 0 then you could do something like.
<?php
    $myArr =  [ 
                'FILE-F01-E1-S01.pdf', 
                'FILE-F01-E1-S02.pdf', 
                'FILE-F01-E1-S03.pdf', 
                'FILE-F01-E1-S04.pdf', 
                'FILE-F01-E1-S05.pdf', 
                'FILE-F02-E1-S01.pdf', 
                'FILE-F02-E1-S02.pdf', 
                'FILE-F02-E1-S03.pdf'
              ];

    $baseName        = '';
    $allSimilarNames = [];

    foreach($myArr as $index => &$name) {
      if($index == 0) {
          $baseName = substr($name, 0, strrpos($name, '-'));
          $allSimilarNames[] = $name;
      }
      else {
          if(strpos($name, $baseName) === 0) {
              $allSimilarNames[] = $name;
          }
      }
    }

    var_dump($allSimilarNames);

This will

Check at index one to get the base name to compare against
Loop all items in the array and match all items, no matter where in the array they are, that are similar according to your naming convention

So if you next time have an array that is
$myArr =  [ 
                    'FILE-F02-E1-S01.pdf',
                    'FILE-F01-E1-S01.pdf', 
                    'FILE-F01-E1-S02.pdf', 
                    'FILE-F01-E1-S03.pdf', 
                    'FILE-F01-E1-S04.pdf', 
                    'FILE-F01-E1-S05.pdf', 
                    'FILE-F02-E1-S02.pdf', 
                    'FILE-F02-E1-S03.pdf'
                  ]; 

this will return all the items that match FILE-F02-E1*.
You could also make a small function of it for easier use and not have to rely on the element at index 0 having to be the "base" name.
<?php
function findMatches($baseName, &$names) {
    $matches = [];
    $baseName = substr($baseName, 0, strrpos($baseName, '-'));
    foreach($names as &$name) {
        if(strpos($name, $baseName) === 0) {
          $matches[] = $name;
        }
    }

    return $matches;
}

$myArr =  [ 
            'FILE-F01-E1-S01.pdf', 
            'FILE-F01-E1-S02.pdf', 
            'FILE-F01-E1-S03.pdf', 
            'FILE-F01-E1-S04.pdf', 
            'FILE-F01-E1-S05.pdf', 
            'FILE-F02-E1-S01.pdf', 
            'FILE-F02-E1-S02.pdf', 
            'FILE-F02-E1-S03.pdf'
          ];

$allSimilarNames = findMatches('FILE-F01-E1-S01.pdf', $myArr);

var_dump($allSimilarNames);

