people-you-might-know

Personal algorithm to find people you might know inspired by what I can feel on Facebook and Linkedin. I did it for a technical test within 5 hours. I know this is not perfect, I'll try to improve it later.

How does it work?

We can find people we might know with comparing the following criterias: 
	- Work
	- School
	- Location
	- Mutual friends
	- Profile visiting
	- Tagged pictures together
	- Age range

I "emulate" a database in csv files
Then I run the algo

Run the script

You can launch it via a terminal:
	php index.php [user_id] [nb_show]
		[user_id] is the iduser's you want see possible match
		[nb_show] how many matches you want see

Algorithm

- We give weight to each criteria (config.php)
- We chose a user
- I give a score to all the users in database. The higher score, the more you might know the guy
	
Implementation:
	- Iterate on every users to find if the user match together on criterias:
	- Compare if the other user have the same: work, school, location
	- Count the number of common friends
	- Count the number the other visited my page
	- Count how many time we were tagged together on pictures
	- Calcultate the age range of people. We usually are friends with people who are the same age
	
	Of course the scoring is completely arbitrary. For example, I decide:
		If they were tagged together, I multiply the weight * number of picture together

Some optimisations I did: 
	- setting the value as a key of the array and using isset instead of searching everytime in array is much faster (pymk.php, line 181, 103)
	- isset is faster than array_keys_exist
Some optimisation I could do:
	- Only iterate one time on every user.
	- Find friends level 2
	- Find interrests of people
	- A better scoring system
	- How many comment the user publish on your account (if public profile)
	- If you're friend a long time with someone, we can suggest you some random friends

Recommandations for huge database:

- On bigger database we couldnt iterate on every users. The best choice is to limit it to level 3 connecition of the users.
- Use memcached to store value, and avoid the repetitive databases requests.
- A good code is not enough to support millions of users, a good server architecture is also required. I would suggest:
	Servers:
		- Server A:
			- With a CDN (akamai for example). The end user will get the statics content with the nearest server.
			- Use memcached on local, to have instant answer of the website and avoid ping
		- Server B: database 
		- Server C: Run the script. Take informations on
	How? : 
		The Server C copy the database from server B every x hours. 
		Then, it runs the "People you might Know" script and save the result in Server A (memcached)
		The server A just request with a simple known key getted in server B (we avoid big database request in Server B)