Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

friends.php

The module that shows a user’s friends and followers is Example 21-10, friends.php. This interrogates the friends table just like the members.php program, but only for a single user. It then shows all of that user’s mutual friends and followers, along with the people he is following.

All the followers are saved into an array called $followers and all the people being followed are placed in an array called $following. Then a neat piece of code is used to extract all those that are both following and followed by the user, like this:

$mutual = array_intersect($followers, $following);

The array_intersect function extracts all members common to both arrays and returns a new array containing only those people. This array is then stored in $mutual. Now it’s possible to use the array_diff function for each of the $followers and $following arrays to keep only those people who are not mutual friends, like this:

$followers = array_diff($followers, $mutual);
$following = array_diff($following, $mutual);

This results in the array $mutual containing only mutual friends, $followers containing only followers (and no mutual friends), and $following containing only people being followed (and no mutual friends).

Armed with these arrays, it’s a simple matter to separately display each category of members, as can be seen in Figure 21-6. The PHP sizeof function returns the number of elements in an array; here I use it just to trigger code when the size is nonzero (that is, when friends of that ...