Similar to the below, rewriting to not use the object creation inside the loop...

```ruby
redis.zrange("failed_checks", 0, -1).inject({}) do |memo, key|
  entity, check = key.split(':', 2)
  if !!redis.zscore("current_checks:#{entity}", check)
    memo[entity] ||= []
    memo[entity] << check
  end
  memo  
end
```