group_by could support compounded expressions like max(v1) - min(v2)

Description

I would like to compute an expression by group which is compounded from two aggregates "max v1 - min v2 by id3".
API that could eventually works, using R syntax
```
h2o.group_by(hf, by="id3", max("v1") - min("v2"))
```
raises exception now

Assignee

New H2O Bugs

Fix versions

None

Reporter

Jan Gorecki

Support ticket URL

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Affected Spark version

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Customer Request Type

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Task progress

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CustomerVisible

No

Priority

Major
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