# Supported Zarr features in Rarr

## Zarr version

Rarr supports both Zarr version 2 and Zarr version 3 but some version 3 features are still a work in progress. In particular, it is known that the sharding codec is not yet implemented.

## Reading and Writing

Reading Zarr arrays is reasonably well supported. Writing is available, but is more limited. Both aspects are under active development.

### Stores

Store Type | Status (reading / writing) | Notes
--- | --- | ---
`FilesystemStore` | ✔ / ✔ |
`S3Store` | ✔ / ❌ |

### Data Types

Currently there is only support for reading and writing a subset of the possible datatypes that can be found in a Zarr array. In some instances there are also limitations on the datatypes natively supported by R, requiring conversion from the Zarr datatype. The table below summarises the current status of datatype support. It will be updated as progress is made.

Zarr Data Type | Status (reading / writing) | Notes
--- | --- | ---
`boolean` | ✔ / ✔ | (via `{grumpy}`)
`int8` | ✔ / ✔ | (via `{grumpy}`)
`uint8` | ✔ / ✔ | (via `{grumpy}`)
`int16` | ✔ / ✔ | (via `{grumpy}`)
`uint16` | ✔ / ✔ | (via `{grumpy}`)
`int32` | ✔ / ✔ | (via `{grumpy}`)
`uint32` | ✔ / ✔ | (via `{grumpy}`)
`int64` | ✔ / ✔ | (via `{grumpy}`)
`uint64` | ✔ / ✔ | (via `{grumpy}`)
`half` / `float16` | ✔ / ❌ | (via `{grumpy}`)
`single` / `float32` | ✔ / ✔ | (via `{grumpy}`)
`double` / `float64` | ✔ / ✔ | (via `{grumpy}`)
`complex` | ❌ / ❌ |
`timedelta` | ❌ / ❌ |
`datetime` | ❌ / ❌ |
V2 `string` | ✔ / ✔ | (via `{grumpy}`)
V3 `null_terminated_bytes` | ✔ / ✔ | (via `{grumpy}`)
V2 `Unicode` | ✔ / ✔ | (via `{grumpy}`)
V3 `fixed_length_utf32` | ✔ / ✔ | (via `{grumpy}`)
`void *` | ❌ / ❌ |
V2 structured data types | ✔ / ❌ | (via `{grumpy}`)
V3 structured data types | ✔ / ❌ | This type is superseded by V3 struct data types.and the specification says implementation MUST NOT implement writing. (via `{grumpy}`)
V3 struct data types | ✔ / ❌ | (via `{grumpy}`)

### Codecs

#### Compression codecs

Library | Status (reading / writing) | Notes
--- | --- | ---
`zlib / gzip` | ✔ / ✔ |
`bzip2` | ✔ / ✔ |
`blosc` | ✔ / ✔ |
`LZMA` | ✔ / ✔ |
`LZ4` | ✔ / ✔ |
`Zstd` | ✔ / ✔ |

Please open an issue if support for a required compression codec is missing.

#### Other codecs

Codec | Status (reading / writing) | Notes
--- | --- | ---
`endian` | ✔ / ❌ | (via `{grumpy}`)
`transpose` | ✔ / ✔ |
`VLen-UTF8` | ✔ / ✔ * | Writing supported only via `update_zarr_array()`

### Optional fields or features

Feature | Status (reading / writing) | Notes
--- | --- | ---
`dimension_names` | ✔ / ✔ | Corresponds to `names(dimnames(x))` in R