How to calculate cumulative sum in PHP? - php

Question

I want to calculate the sum and output a two columns table. But, the format is wrong. The numbers are all packed in one line.
<td>
<?php
for ($j = 1; $j <= 10; $j++)
{
print "<tr>";
print $j;
print "</tr>";
}
?>
</td>
<td>
<?php
$sum = 0;
for($i = 1; $i<=10; $i++)
{
print "<tr>";
print $sum = $sum + $i;
print "</tr>";
}
?>
</td>

Answer 1

Here, we would be writing one or two for loops, join our desired HTML string, and finally we would print it.
Test:
<?php
$html = '<tr>';
for ($j = 1; $j <= 10; $j++) {
$html .= "<td>" . $j . "</td>";
}
$html .= '</tr>';
$html .= '<tr>';
$sum = 0;
for ($i = 1; $i <= 10; $i++) {
$sum += $i;
$html .= "<td>" . $sum . "</td>";
}
$html .= '</tr>';
print($html);
?>
We would be also adding table open and close tags (<table>, </table>):
<?php
$html = '<table>';
$html .= '<tr>';
$html .= "<td>Number</td>";
for ($j = 1; $j <= 10; $j++) {
$html .= "<td>" . $j . "</td>";
}
$html .= '</tr>';
$html .= '<tr>';
$html .= "<td>Cumulative Sum</td>";
$sum = 0;
for ($i = 1; $i <= 10; $i++) {
$sum += $i;
$html .= "<td>" . $sum . "</td>";
}
$html .= '</tr>';
$html .= '</table>';
print($html);
?>
For two columns, we would just use one for` loop:
<?php
$html = '<table>';
$html .= "<tr><th>Number</th><th>Cumulative Sum</th></tr>";
for ($j = 1; $j <= 10; $j++) {
$html .= "<tr>";
$html .= "<th>" . $j . "</th>";
$sum += $j;
$html .= "<th>" . $sum . "</th>";
$html .= "</tr>";
}
$html .= '</table>';
print($html);

Answer 2

I ended up here when looking to get a cumulative sum in PHP. For the ones like me, I wrote the following function. It's safe for empty arrays as well.
function cumsum ($arr) {
return array_reduce($arr, function ($c, $i) { $c[] = end($c) + $i; return $c; }, []);
}