Allow type override in := when i is just order()
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Assessment
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Newbie friendliness
- 45/100
Research direction
Start by reproducing the two data.table examples in the issue and compare how := handles a non-empty order-only i expression. Locate the relevant := update path and add a regression test showing that assigning paste0(a) after order(-a) no longer raises the type-override error.
Written by the indexing model from the issue text.
Description
DT = data.table(a = 1:10)
DT[order(-a), a := paste0(a)]
This errors saying we should be explicit about type overrides, but:
DT[ , a := paste0(a)]
This code works fine (and is of course identical, but the same problem arises when the column update is order-dependent). Presumably this is because when i is non-empty, := suspects there could be a type collision if assigning a new type to a subset of rows.
But order queries in i are incapable of subsetting, so I would expect the behavior to be identical.
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