westonpace commented on issue #15042:
URL: https://github.com/apache/arrow/issues/15042#issuecomment-1369130318
It appears the null count is also wrong. From a glance, the dictionary
writing path (`WriteArrowDictionary` in `column_writer.cc`) looks something
like this:
```
if (AlreadyHaveDictionaryForColumn()) {
if (IsDictionaryChanged()) {
# Fallback to plain or maybe unify or something
} else {
# Write another indices batch
}
} else {
# Calculate statistics / null count and setup column and store dictionary
for future write to column
}
```
So I suppose the behavior makes sense given the above algorithm. We need to
add "update null count and potentially update min/max" to that middle branch.
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