<?php
// $columns is built-in. It's an associative array. We're getting the value of the "name" column.
$full_name = $columns['name']['value'];

// Let's break it apart so we can separate the first and last name
$full_name = explode(' ', $full_name);

// This logic can be improved. Right now, it simply assumes that the last name is the last element in the $full_name array
// E.g. $full_name = array('Billy', 'Bob', 'Thornton');
// $first_name is $full_name[2], aka "Thornton".
$first_name = $full_name[count($full_name) - 2];

// Pass that back into the $columns array for the "first_name" column
$columns['first_name']['value'] = $first_name;