mars-project / mars-project/mars
`groupby` could be executed twice when eager mode is on for `df.groupby().agg()`
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mod: dataframe
type: enhancement
- Dominant language
- Python
- Stars
- 2.7k
- Forks
- 325
- PR merge metrics
- No merged PRs in 30d
Description
For `df.groupby().agg()`, when eager mode is on, `groupby` may be executed twice, that's because `agg` would do map-combine-aggregate or map-reduce whenever the `groupby` has been executed or not.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by locating the implementation of DataFrame groupby().agg() and the eager-execution path described in the issue. Trace whether groupby runs before aggregation and inspect any related tests. Done means eager mode executes groupby only once while preserving the expected aggregation result.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- data
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100