open Deedle
open Deedle.Arrow

// Convert between Deedle and Arrow in-memory
Frame.toRecordBatch : Frame<'R,'C> -> RecordBatch
Frame.ofRecordBatch : RecordBatch  -> Frame(int,string)

// Arrow IPC file format  (.arrow / .feather)
Frame.readArrow  : string -> Frame(int,string)
Frame.writeArrow : string -> Frame<'R,string> -> unit

// Arrow IPC stream format  (.arrows)
Frame.readArrowStream  : Stream -> Frame(int,string)
Frame.writeArrowStream : Stream -> Frame<'R,string> -> unit

// Row-key preservation
Frame.writeArrowWithIndex : string -> Frame<'R,string> -> unit
Frame.readArrowWithIndex  : string -> Frame(string,string)

// Feather v2 aliases
Frame.readFeather  : string -> Frame(int,string)
Frame.writeFeather : string -> Frame<'R,string> -> unit

Series.toArrowArray : Series<'K,'V> -> IArrowArray
Series.ofArrowArray : IArrowArray   -> Series(int,obj)
```

The existing free functions (`readArrow`, `writeArrow`, `frameToRecordBatch`, etc.) are still present for backward compatibility.

---

## Extended test suite

All new tests are in `tests/Deedle.Arrow.Tests/Tests.fs`. Added **29 new tests** on top of the existing 24, bringing the total to **53 tests**:

| Category | Tests |
|---|---|
| Frame module API | 5 |
| Series module API | 5 |
| Edge cases | 8 |
| FsCheck property-based | 5 |
| (existing Part 1 + Part 2) | 30 |

Edge cases covered: single row, single column, all-missing column, mixed-type frame, int64 stream, float32 file, empty-string column.

FsCheck properties: `float` round-trip, `int` round-trip, `string` round-trip, Series round-trip, RecordBatch column-name preservation.

---

## New documentation pages

### `docs/arrow.fsx` — Apache Arrow and Feather integration
- Reading and writing Arrow / Feather files (`Frame.readArrow`, `Frame.writeArrow`, etc.)
- Arrow IPC stream format
- Converting to/from `RecordBatch`
- Series ↔ Arrow array conversion
- Row-key preservation with `writeArrowWithIndex` / `readArrowWithIndex`
- Full type mapping table
- Python / pyarrow interoperability examples
- NuGet package information

### `docs/joining.fsx` — Joining, merging and appending frames
- Outer / inner / left frame joins
- Lookup joins with `Lookup.ExactOrSmaller` / `ExactOrGreater`
- Series zipping with `Series.zip` / `Series.zipInto`
- Appending frames vertically with `Frame.merge`
- Merging sparse series with `Series.merge`

---

## Remaining documentation (filed separately)

Issue #684 tracks the remaining documentation gaps: missing-value handling, `Deedle.Math`, `Deedle.Excel`, grouping deep-dive, and C# API docs. Contributions are welcome.

---

## Test status

```
Deedle.Arrow.Tests   — Passed! Failed: 0, Passed: 53, Skipped: 0
Deedle.Tests (core)  — Passed! Failed: 0, Passed: 690, Skipped: 0