Needs libpqxx

/etc/postgresql/11/main/pg_hba.conf

# IPv4 local connections:
host    all         all         127.0.0.1/32          md5

service postgresql restart or /etc/init.d/postgresql restart

creating a sparse matrix for the algorithm:

make two vectors -- these will map users and movies to the matrix (make these vectors into a lists, so they would be resizable)
* can we also make matrix resizable?

go through all ratings, if movie or user was already seen, proceed further, otherwise, add those