Clarify .I behavior for non-matching rows in joins with by = .EACHI #7258
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #7258 +/- ##
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ben-schwen
reviewed
Aug 22, 2025
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| The reason for this difference is crucial: | ||
| - In Case 1, we are performing a value lookup. A failed lookup results in a missing value (`NA`). | ||
| - In Case 2, we are performing an evaluation. The symbol `.I` is defined as "the row indices in `x` for the current group". For non-matching rows like `D`, the group of matching rows in d1 is empty. The set of indices for an empty group is integer(0). data.table represents this zero-length result as a single `0` in the output. |
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where does this info come from?
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Not sure |
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Tbh I would also rather fix it than adopting documentation. edit: this should then also close #3452 |
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closes #5457
this pr
Clarifies
.Idocs in joins withby = .EACHI:Column lookup = NA
.I/.Non unmatched groups → 0Docs updated, no behavior change.
hi @MichaelChirico @tdhock can you please have a look when you got time
thanks.