pitrou commented on PR #37418:
URL: https://github.com/apache/arrow/pull/37418#issuecomment-1735426328
This doesn't need to be a compute function. There are already dict-related
utilities in `src/arrow/array/array_dict.h` (including
`DictionaryArray::Transpose` which is certainly useful here).
So I would recommend something like:
```c++
class DictionaryArray {
/// Return a transpose map to remove any unused dictionary entries.
Result<std::vector<int32_t>> Compact() const;
};
```
Or perhaps (similar idea but using the Arrow C++ allocators rather than the
STL):
```c++
class DictionaryArray {
/// Return a transpose map to remove any unused dictionary entries.
/// \result the transpose map as a buffer of int32 values
Result<std::shared_ptr<Buffer>> Compact() const;
};
```
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