Most of the time, if you need to create an HTML table to display data pulled from a database, it’s a fairly straightforward task: the data is organized in rows, and since HTML tables are generated in rows, it’s easy to loop through the rows of data and display them in succession. But sometimes you can have a situation where you want to display the data as columns, which is not something you can easily do in HTML. Here’s an example of how to approach this challenge.

Displayed below is an array of data from a project I’ve been working on. I’ll explain the color coding in a minute. The first element is a sub array of laboratory sample IDs, and the subsequent elements are subarrays indicating which laboratory tests should be run on which samples. (I’ll spare you an explanation of the database structure behind all this, but suffice it to say that pulling out the data with this organization was the most efficient solution).

Array[4] (
    0 => Array[6] (
        0 => 'Sample ID',
        1 => 193,
        2 => 194,
        3 => 195,
        4 => 196,
        5 => 197,
    ),
    1 => Array[4] (
        0 => 'Phospholipids',
        1 => 'Y',
        3 => 'Y',
        5 => 'Y',
    ),
    2 => Array[6] (
        0 => 'Apolipoprotein A-I',
        1 => 'Y',
        2 => 'Y',
        3 => 'Y',
        4 => 'Y',
        5 => 'Y',
    ),
    3 => Array[4] (
        0 => 'Gastrin',
        2 => 'Y',
        3 => 'Y',
        4 => 'Y',
    ),
)

How I ultimately what to display the data is like this:

To get from here to there, you need to visualize how you want to arrange the data elements. If you use the color coding I assigned to the array indexes above, you can picture the data in rows, like this:

0,0    1,0    2,0    3,0

0,1    1,1    2,1    3,1

etc.

To generate a display of the data in this manner, you need to loop through the arrays in an inside-out manner. You loop through the subarrays to set the rows, and then have a nested loop through the parent array to set the cells. Here’s the PHP code for it:

$content = "<table>\n";

// This loop controls the table rows
// $cols is the name of the parent array
for ($inner=0; $inner < count($cols[0]); $inner++) {
    $content .= "<tr>";

    // This loop generates the table cells
    for ($outer=0; $outer < count($cols); $outer++) {
        // this assumes you want the first row to be a header row
        $tag = ($inner == 0) ? "th" : "td";  
        $content .= "<$tag>{$cols[$outer][$inner]}</$tag>";  
    }

    $content .= "</tr>\n";
}

$content .= "</table>\n";

// then display or return $content...

The first subarray contains the Sample IDs, so I used it to set the maximum count for the outer loop that controls the HTML table rows (because I can be confident there will never be data beyond the last sample). If you don’t have an analogous subarray, you’ll need to check to see which subarray is longest, and use that to control the count.