code: public static int getPartitionStatic(LongWritable key, LongWritable value,
        int numPartitions) {
      return (int) (Math.abs(key.get()) % numPartitions);
    }
docs: Get a partition from the key only
  @param key Key to partition
  @param value Value (not used)
  @param numPartitions Number of partitions
  @return Destination partition