JerAguilon commented on code in PR #41874:
URL: https://github.com/apache/arrow/pull/41874#discussion_r1619131719
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cpp/src/arrow/acero/unmaterialized_table.h:
##########
@@ -204,15 +231,79 @@ class UnmaterializedCompositeTable {
return builder.Append(data + offset0, offset1 - offset0);
}
+ arrow::Result<std::vector<CompositeEntry>> FlattenSlices(int table_index) {
+ std::vector<CompositeEntry> flattened_blocks;
+
+ arrow::RecordBatch* active_rb = NULL;
+ size_t start = -1;
+ size_t end = -1;
+
+ for (const auto& slice : slices) {
Review Comment:
If it's not self-evident, the asof-join works by creating a `CompositeEntry`
for each output row.
Since these so-called "contiguous inputs" are `Slice`able, we squash these
entries down. For example, suppose `slices` has a LHS table that looks like
this:
```
{rb_addr: 1234, start: 1, end: 2},
{rb_addr: 1234, start: 2, end: 3},
{rb_addr: 1234, start: 3, end: 4},
{rb_addr: 4321, start: 100001, end: 100002},
{rb_addr: 4321, start: 100002, end: 100003},
```
This function will squash this down to a compact vector:
```
{rb_addr: 1234, start: 1, end: 4},
{rb_addr: 4321, start: 100001, end: 100003},
```
Which we can quickly use to slice the appropriate output column(s).
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