Redis Sorted Set: Bulk ZSCORE - ruby

Question

How to get a list of members based on their ID from a sorted set instead of just one member?
I would like to build a subset with a set of IDs from the actual sorted set.
I am using a Ruby client for Redis and do not want to iterate one by one. Because there could more than 3000 members that I want to lookup.
Here is the issue tracker to a new command ZMSCORE to do bulk ZSCORE.

Answer 1

There is no variadic form for ZSCORE, yet - see the discussion at: https://github.com/antirez/redis/issues/2344
That said, and for the time being, what you could do is use a Lua script for that. For example:
local scores = {}
while #ARGV > 0 do
scores[#scores+1] = redis.call('ZSCORE', KEYS[1], table.remove(ARGV, 1))
end
return scores
Running this from the command line would look like:
$ redis-cli ZADD foo 1 a 2 b 3 c 4 d
(integer) 4
$ redis-cli --eval mzscore.lua foo , b d
1) "2"
2) "4"
EDIT: In Ruby, it would probably be something like the following, although you'd be better off using SCRIPT LOAD and EVALSHA and loading the script from an external file (instead of hardcoding it in the app):
require 'redis'
script = <<LUA
local scores = {}
while #ARGV > 0 do
scores[#scores+1] = redis.call('ZSCORE', KEYS[1], table.remove(ARGV, 1))
end
return scores
LUA
redis = ::Redis.new()
reply = redis.eval(script, ["foo"], ["b", "d"])
Lua script to get scores with member IDs:
local scores = {}
while #ARGV > 0 do
local member_id = table.remove(ARGV, 1)
local member_score = {}
member_score[1] = member_id
member_score[2] = redis.call('ZSCORE', KEYS[1], member_id)
scores[#scores + 1] = member_score
end
return scores