How do I get the rank / row number for a row?

问题:

Is there a way to get the row numbers (rank) for a filtered set and append the row number to the result?

An example scenario would be that I have a table with records like:

[ 
  { points: 123, name: 'Glenn' },
  { points: 948, name: 'Bob' },
  { points: 22, name: 'Sarah' }
]

In the above table there are hundreds of thousands of rows, and I want to be able to rank all records based on a condition like points descending and then return a subset of the rows (using a filter) with their rank value included in the result like this:

[ { points: 123, name: 'Glenn', rank: 2 }]

回答1:

You should use the offsetsOf function

r.table('users') .orderBy({index: 'points'}) .offsetsOf(r.row('user_id').eq(yourUserId)) .run(conn, callback)

Command Reference: http://rethinkdb.com/api/javascript/offsets_of/

回答2:

r.table('users').orderBy({index: 'points'}).run(conn, callback)

Tis will return the list sorted by points. (Ie: The first element will have rank 1, the second element rank 2, etc.)

See also: https://rethinkdb.com/api/javascript/order_by/

回答3:

The .map function accept one or more sequences/arrays (See Docs). So you can use your filtered sequence for first argument and use r.range() as second parameter. So your callback function will have 2 arguments (each one representing an element of one sequence/array). See below:

r.table('users')
    .orderBy({index: 'points'})
    .map(r.range(), (user, number) => {
        return user.merge(rank: number.add(1))
    }