Group multidimensional array by key and sum values in PHP - php

Question

There are similar questions on Stack Overflow but nothing quite like mine, and I also want to double check that I am doing this the most efficient way (resource wise).
I have surveys that are submitted and I want to tally the results. Each survey is saved in a multidimensional array like so:
Array ( [name] => Clark Kent [rating] => 5 )
These are coming from a loop as they are separate database entries.
So I am beginning by creating a new array with all these combined:
$mods = array();
$index = -1;
foreach($fields as $field) {
$index++;
$mods[$index]['name'] = $field['name'];
$mods[$index]['rating'] = $field['rating'];
}
Then I am grouping these so that all the ratings for the same name are together, so I can sum them later.
$groups = array();
foreach ($mods as $value) {
$groups[$value['name']][] = $value;
}
This produces the following:
Array (
[Clark Kent] => Array (
[0] => Array (
[name] => Clark Kent
[rating] => 5
)
[1] => Array (
[name] => Clark Kent
[rating] => 5
)
)
[Peter Parker] => Array (
[0] => Array (
[name] => Peter Parker
[rating] => 5
)
[1] => Array (
[name] => Peter Parker
[rating] => 5
)
)
[Bruce Wayne] => Array (
[0] => Array (
[name] => Bruce Wayne
[rating] => 5
)
[1] => Array (
[name] => Bruce Wayne
[rating] => 5
)
)
[Bruce Banner] => Array (
[0] => Array (
[name] => Bruce Banner
[rating] => 5
)
[1] => Array (
[name] => Bruce Banner
[rating] => 5
)
)
)
What I am trying to accomplish would be something like this:
<table>
<tr>
<td>Clark Kent</td>
<td>{average of all ratings}</td>
</tr>
</table>
I'm most of the way there, but I am stuck! I'm not sure how to get the grouped name that doesn't have any type of index or key so I can use that value for my table. Then I need to sum each grouped values.

Answer 1

I would do all the necessary math in the loop that reads the data from the database. Something like this:
$ratings = array();
while ($row = $result->fetch_assoc()) {
$name = $row['name'];
if (!isset($ratings[$name])) {
$ratings[$name] = array('count' => 1, 'sum' => $row['rating']);
}
else {
$ratings[$name]['count']++;
$ratings[$name]['sum'] += $row['rating'];
}
}
Then you can just output your table like so:
echo "<table>";
foreach ($ratings as $name => $r) {
echo "<tr><td>$name</td><td>" . round($r['sum'] / $r['count'], 1) . "</td></tr>";
}
echo "</table>";

Answer 2

To get average you can do something like:
foreach ($groups as $name => $group) {
$average = array_sum(array_column($group, 'rating')) / count($group);
echo $name;
}

Answer 3

You could simplify the problem in the first place in the structure you are using to handle those date
foreach($fields as $field) {
$mods[$field['name']][] = $field['rating'];
}
then just foreach with the key parameter
foreach($mods as $name => $mod) {
echo $name;
echo array_sum($mod) / count($mod);
}

Answer 4

Try to use the code below. Eliminating an extra loop to preparing group array.
$mods = array();
foreach($fields as $field) {
$mods[$field['name']][] = $field['rating'];
}
<table>
<tr>
<?php
if($mods) {
foreach($mods as $key=>$value) {
?>
<td><?php echo $key; ?></td>
<td><?php echo (array_sum($value)/count($value)); ?></td>
<?php
}
}
?>