zeroshade commented on issue #41284:
URL: https://github.com/apache/arrow/issues/41284#issuecomment-2100866694
@candiduslynx I'm very confused by that file, it looks like you're using a
builder to make a deep copy of the arrays which doesn't make any sense to me.
You have this function:
```go
func slice(r arrow.Record) []arrow.Record {
res := make([]arrow.Record, r.NumRows())
for i := int64(0); i < r.NumRows(); i++ {
res[i] = r.NewSlice(i, i+1)
}
return res
}
```
If I'm reading this right, you're slicing the record int a slice of records
of exactly 1 row each? Why?
But I'm more confused by this `reverseTransformArray` function.
`reverseTransformRecord` appears to loop through the columns and call
`reverseTransformArray` with each column's type and the column itself. Which
means that `reverseTransformArray` is receiving a datatype which is always
identical to the datatype of the Array being passed in. This means that
something like `reverseTransformFromString` is always called with a string
array. So you're creating a builder and building up a new array which is
*identical* to the one that was passed in rather than just calling `.Retain()`
on the array and returning the same array that was passed in or using the
`.Copy` method on the `ArrayData` object and then using `MakeFromData`. If you
*really* wanted to make a deep copy (but why??), you could do it in a generic
way by explicitly copying the buffers regardless of the type to create new
ArrayData objects.
> offset should also be used (as the passed in record/array may be sliced),
but not for struct arrays (they are special & I don't know why).
What do you mean "special"? The offset handling for struct arrays should
work precisely the same as any other type. Can you elaborate on what the issue
there is?
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