mapreduce:iterable iteration can only iterate once

When learning Hadoop's mapreduce, the reduce stage should use iterable to iterate the K:V key-value pairs passed in the map stage

But there is a problem, iterable can only iterate once and cannot go back

If multiple loops are required

You can use a collection such as list or map to store the content when iterating

After that, the information in the collection can be called in a loop