One thing that I considered some time ago was working out which are the most common functions in a language and adding this as an additional signal to ranking. I couldn't find anywhere else on the web with this question answered so I took my own approch. The method was to take a collection of large PHP projects, including, Wordpress, Mambo, Sphider, Smarty, Drupal, CodeIgniter, dump all their source code into a single file stripped of comments, and then run some simple regex over this file counting the occurance of each function.

His results show the top five as: array, isset, define, empty and assert. The last five ended up being: filemtime, sha1, array_unshift, get_current_user and strchr.

When scripting in PHP, we often restrict ourselves to a limited number of API functions: the common ones, like print(), header(), define(), isset(), htmlspecialchars(), etc. [...] The PHP API actually offers a lot of functionality, some useless and some useful; often seldom used. I have been looking through the available functions and was interested to find some really cool functions that I should have known about.

Here's his list of functions, some of which are more on the "special needs" list than the "never use" list:

• sys_getloadavg
• pack
• cal_days_in_month
• _()
• get_browser
• debug_print_backtrace
• metaphone
• natsort
• levenshtein
• glob