PHP foreach to nest list with variable elements at each level?

Question

I'm still learning PHP, and have started to understand the working of foreach() loop. I am stuck on something.

I'm working with PHP drawing from a MySQL database, and I want to list how many items share the same "topic_id". With the initial number, I'm trying to make a nested list that identifies what different medium types each item is available in, and how many items are counted in each medium.

This is the database query I'm using:

SELECT 
  m.name AS medium, i.medium_id, f.name AS format, 
  SUM(
    CASE WHEN it.topic_id = '$topicId' AND i.id = it.item_id 
      THEN 1 
      ELSE 0 END
  ) AS sumFormat
FROM items AS i
LEFT JOIN item_topics AS it 
  ON i.id = it.item_id 
LEFT JOIN formats AS f 
  ON f.id = i.format_id 
LEFT JOIN media AS m 
  ON m.id = i.medium_id 
GROUP BY medium, format 
ORDER BY medium ASC

This gives the following result (I've omitted sumFormat=0 results):

+--------------+-------------+--------------+-----------+
| medium       | medium_id   | format       | sumFormat |
+--------------+-------------+--------------+-----------+
| Games        |           1 | NULL         |         1 |
| Magazines    |           2 | Paperback    |        35 |
| Albums       |           3 | CD           |        25 |
| Albums       |           3 | Record       |         1 |
| Books        |           5 | Audiobook    |        38 |
| Books        |           5 | Diary        |         1 |
| Books        |           5 | Dictionary   |         4 |
| Books        |           5 | Ebook        |       421 |
| Books        |           5 | Hardback     |        76 |
| Books        |           5 | Paperback    |       574 |
| Comics       |           6 | Paperback    |         2 |
+--------------+-------------+--------------+-----------+

Depending on the "$topicId" being queried, the results will be different - in some cases, there might not be any items in a given medium or format. I'd like the PHP code to handle this, so only the medium types and formats that are present for the "topic_id" will be listed.

In my PHP code, I've put it together like so:

<ul id="formats">
<?php foreach ($topicFormats as $topicFormat): ?>
    <?php if ($topicFormat['medium'] && $topicFormat['sumFormat']): ?>
        <li><?= $topicFormat['medium'] ?></li>
            <?php if ($topicFormat['sumFormat']): ?>
                <ul>
                <li><?= $topicFormat['sumFormat'] ?>
                    <?php if (!$topicFormat['format']): ?>
                        Games
                    <?php else: ?><?= $topicFormat['format'] ?>
                        <?php endif; ?>
                </li>
                </ul>
            <?php endif; ?>
    <?php endif; ?>
<?php endforeach; ?>

The final HTML looks like this:

    1178 Items
    • Games
        • 1 Games
    • Magazines
        • 35 Paperback
    • Albums
        • 1 Record
    • Albums
        • 25 CD
    • Books
        • 38 Audiobook
    • Books
        • 1 Diary
    • Books
        • 4 Dictionary
    • Books
        • 421 Ebook
    • Books
        • 76 Hardback
    • Books
        • 574 Paperback
    • Comics
        • 2 Paperback

However I want the result below:

    1178 Items
    • Games
        • 1 Games
    • Magazines
        • 35 Paperback
    • Albums
        • 1 Record
        • 25 CD
    • Books
        • 38 Audiobook
        • 1 Diary
        • 4 Dictionary
        • 421 Ebook
        • 76 Hardback
        • 574 Paperback
    • Comics
        • 2 Paperback

I have checked this issue on StackOverFlow but did not find any solution. Any help would be appreciated!

Edit: I haven't had a chance to try out any of your suggestions yet, but in answer to Kapilgopinath, here is the resultant array (I think this is what you're asking for - I've never retrieved a resultant array before!):

Array 
(
[0] => Games
[medium] => Games
[1] => 1 
[medium_id] => 1 
[2] => 
[format] => 
[3] => 1 
[sumFormat] => 1 
)

("Games" doesn't have a format, so it returns null - that would be where other medium types would list "Paperback", "CD", etc.)

I would just only put out the ul tag in the loop if the value of medium has changed. — Kickstart
– Kickstart, Commented May 22, 2014 at 8:47
This is possible by grouping the resultant array. Can you paste the resultant $topicFormats array. — Kapil gopinath
– Kapil gopinath, Commented May 22, 2014 at 8:51
@Kapilgopinath I've added the resultant array (I hope I did it right!) — Dion
– Dion, Commented May 22, 2014 at 10:00

Ryan Vincent · Accepted Answer · 2014-05-24 22:02:47Z

1

The issue with using a 'foreach' loop is that the next read is not done until the end of the loop, which is too late, when you have a 'nested loop' as here. It can be easier, although not less code, to use a 'read ahead' technique. The advantage is that you do not need an if test to determine what to do with the current entry. Therefore you need an iterator then it is just nested loops. With the read of the next record, immediately after the current one has been processed.

<?php
    $values_from_db = array( array( 'medium' => 'Games', 'format' => 'Games', 'sumFor' => 1, ), array( 'medium' => 'Magazines', 'format' => 'Paperback', 'sumFor' => 35, ), array( 'medium' => 'Albums', 'format' => 'CD', 'sumFor' => 25, ), array( 'medium' => 'Albums', 'format' => 'Record', 'sumFor' => 1, ), array( 'medium' => 'Books', 'format' => 'Audiobook', 'sumFor' => 38, ), array( 'medium' => 'Books', 'format' => 'Diary', 'sumFor' => 1, ), array( 'medium' => 'Books', 'format' => 'Dictionary', 'sumFor' => 4, ), array( 'medium' => 'Books', 'format' => 'Ebook', 'sumFor' => 421, ), array( 'medium' => 'Books', 'format' => 'Hardback', 'sumFor' => 76, ), array( 'medium' => 'Books', 'format' => 'Paperback', 'sumFor' => 574, ), array( 'medium' => 'Comics', 'format' => 'Paperback', 'sumFor' => 2, ), );

    $iterSumFor = new ArrayIterator($values_from_db);
    $curEntry = $iterSumFor->current(); // read ahead -- always a current record to process
?>
<ul>
<?php while ($iterSumFor->valid()): ?>
    <?php $curMedium = $curEntry['medium']; ?>
    <li><?= $curMedium ?></li>
    <ul>
        <?php while ($iterSumFor->valid() && $curEntry['medium'] == $curMedium): ?>
            <li><?= $curEntry['sumFor'], '&nbsp;', $curEntry['format'] ?></li>
            <?php $iterSumFor->next(); ?>
            <?php $curEntry = $iterSumFor->current(); ?>
        <?php endwhile; ?>
    </ul>
<?php endwhile ?>
</ul>

edited May 24, 2014 at 22:02

answered May 22, 2014 at 10:27

Ryan Vincent

4,5137 gold badges24 silver badges33 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Dion Over a year ago

I really appreciate this answer, because it has taught me something new altogether. I have a question, however: this gave the results perfectly, but so did the "foreach" approach that kevinabelita provided. Which, then, is "better"? Does one of these two methods have an advantage over the other?

Ryan Vincent Over a year ago

@Dion, The way to think about it isn't about 'better' or 'best'. It it more that you now have two separate ways of solving a problem that are: 1) similar amounts of code to implement 2) easy to understand and 3) give the correct results. You choose the appropriate way depending on the problem you are trying to solve. Sometime 'read ahead' is easier to use, other times 'foreach'. Both have their uses. 'Read ahead' is usually easier when there are 'nested' loops and the input is a single stream.

user1978142 · Accepted Answer · 2014-05-22 09:01:54Z

1

First off, you need to group the main result of the query first. And from then on, you can loop them and build the list. Here is the general idea, consider this example:

$values_from_db = array( array( 'medium' => 'Games', 'format' => 'Games', 'sumFor' => 1, ), array( 'medium' => 'Magazines', 'format' => 'Paperback', 'sumFor' => 35, ), array( 'medium' => 'Albums', 'format' => 'CD', 'sumFor' => 25, ), array( 'medium' => 'Albums', 'format' => 'Record', 'sumFor' => 1, ), array( 'medium' => 'Books', 'format' => 'Audiobook', 'sumFor' => 38, ), array( 'medium' => 'Books', 'format' => 'Diary', 'sumFor' => 1, ), array( 'medium' => 'Books', 'format' => 'Dictionary', 'sumFor' => 4, ), array( 'medium' => 'Books', 'format' => 'Ebook', 'sumFor' => 421, ), array( 'medium' => 'Books', 'format' => 'Hardback', 'sumFor' => 76, ), array( 'medium' => 'Books', 'format' => 'Paperback', 'sumFor' => 574, ), array( 'medium' => 'Comics', 'format' => 'Paperback', 'sumFor' => 2, ), );

// group them first
$formatted_array = array();
foreach($values_from_db as $key => $value) {
    $formatted_array[$value['medium']][] = $value;
}

$list = '<ul>';
foreach($formatted_array as $key => $value) {
    $list .= "<li>$key</li>";
    if(is_array($value)) {
        $list .= "<ul>";
        foreach($value as $index => $element) {
            $list .= "<li>$element[sumFor] $element[format]</li>";
        }
        $list .= "</ul>";
    }
}
$list .= '</ul>';

print_r($list);

Sample Fiddle

answered May 22, 2014 at 9:01

user1978142

7,9683 gold badges19 silver badges20 bronze badges

1 Comment

Dion Over a year ago

Thank you for this answer - it did give the results, as did Ryan Vincent's answer, which used the "read ahead" technique. Since I'm still learning PHP, is the "read ahead" technique a better overall approach, instead of doing foreach loops?

Kickstart · Accepted Answer · 2014-05-22 08:56:06Z

Doing this by saving the previous value of medium and only outputting the tag when this changes would give something like this (not tested)

<ul id="formats">
<?php 
$prev_medium = '';
foreach ($topicFormats as $topicFormat)
{
    if ($topicFormat['medium'] && $topicFormat['sumFormat'])
    {
        if ($prev_medium != $topicFormat['medium'])
        {
            if ($prev_medium != '')
            {
                echo '</ul>';
                echo '</li>';
            }
            echo '<li>'.$topicFormat['medium'].'</li>';
            echo '<ul>';
            $prev_medium = $topicFormat['medium'];
        }
        if ($topicFormat['sumFormat'])
        {
            echo '<li>'.$topicFormat['sumFormat'];
            echo (($topicFormat['format']) ? $topicFormat['format'] : 'Games' );
            echo '</li>';
        }
    }
}
if ($prev_medium != '')
{
    echo '</ul>';
    echo '</li>';
}
?>
</ul>

In a relatively simple list like this it might be easy to do as Kapil gopinath suggests and group the items in SQL, then just explode them out in the code.

Rakesh Sharma · Accepted Answer · 2014-05-22 08:57:09Z

try

$i =0; $a = array();
<ul id="formats">
<?php foreach ($topicFormats as $topicFormat): ?>
    <?php if ($topicFormat['medium'] && $topicFormat['sumFormat']): ?>
        <li><?php  if(!in_array($topicFormat['medium'], $a)) {
                      $a[$topicFormat['medium']]= $topicFormat['medium'];
                      echo $a[$topicFormat['medium']];
                    }?></li>
            <?php if ($topicFormat['sumFormat']): ?>
                <ul>
                <li><?= $topicFormat['sumFormat'] ?>
                    <?php if (!$topicFormat['format']): ?>
                        Games
                    <?php else: ?><?= $topicFormat['format'] ?>
                        <?php endif; ?>
                </li>
                </ul>
            <?php endif; ?>
    <?php endif; ?>
<?php endforeach; ?>

Kapil gopinath · Accepted Answer · 2014-05-22 09:01:25Z

0

try this.    


<?php foreach ($topicFormats as $topicFormat): ?>
        <?php 
        $medium = $topicFormat['medium'];
        $format = $topicFormat['format']          
        $format[$medium][] = $topicFormat['sumFormat'].' '. $format ? $format : 'Games'; 
        <?php endforeach;        
        echo '<pre>';
        print_r($arr);
?>

answered May 22, 2014 at 9:01

Kapil gopinath

1,0431 gold badge8 silver badges19 bronze badges

Collectives™ on Stack Overflow

PHP foreach to nest list with variable elements at each level?

5 Answers 5

2 Comments

1 Comment

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

2 Comments

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related