The first example is using a rather old version from 2012.
It's bound to have some problems so I've updated the snippet
We need to assign a named stack for the second series to make it clear that we don't want to share the same stack.
We don't check specifically for false and treat "stack: false" as undefined.
This is worth investigating as we have a clearly stated intent that shouldn't be ignored.
This gets us somewhere, but the grouping will generate two series for the second group.
Not sure if this is the desired result.
An alternative would be to update the stack setting on the series after grouping has been done.
The dataBound event
gives us opportunity do this. See this snippet
for a demo.
I hope this helps.
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