Computes the union of numkeys sorted sets given by the specified keys, and
stores the result in destination.
It is mandatory to provide the number of input keys (numkeys) before passing
the input keys and the other (optional) arguments.
By default, the resulting score of an element is the sum of its scores in the sorted sets where it exists.
Using the WEIGHTS option, it is possible to specify a multiplication factor
for each input sorted set.
This means that the score of every element in every input sorted set is
multiplied by this factor before being passed to the aggregation function.
When WEIGHTS is not given, the multiplication factors default to 1.
With the AGGREGATE option, it is possible to specify how the results of the
union are aggregated.
This option defaults to SUM, where the score of an element is summed across
the inputs where it exists.
When this option is set to either MIN or MAX, the resulting set will contain
the minimum or maximum score of an element across the inputs where it exists.
If destination already exists, it is overwritten.
@return
@integer-reply: the number of elements in the resulting sorted set at
destination.
@examples
ZADD zset1 1 "one"
ZADD zset1 2 "two"
ZADD zset2 1 "one"
ZADD zset2 2 "two"
ZADD zset2 3 "three"
ZUNIONSTORE out 2 zset1 zset2 WEIGHTS 2 3
ZRANGE out 0 -1 WITHSCORES