# Supported Zarr features in Rarr

## Zarr version

Rarr currently only works with Zarr specification version 2. Support for version 3 is actively being worked on.

## Reading and Writing

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

### 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` | ✔ / ✔ |
`int8` | ✔ / ❌ |
`uint8` | ✔ / ✔ |
`int16` | ✔ / ✔ |
`uint16` | ✔ / ❌ |
`int32` | ✔ / ✔ |
`uint32` | ✔ / ❌ | Values outside the range of `int32` are converted to `NA`. Future plan is to allow conversion to `double` or use the bit64 package.
`int64` | ✔ / ❌ | Values outside the range of `int32` are converted to `NA`. Future plan is to allow conversion to `double` or use the bit64 package.
`uint64` | ✔ / ❌ | Values outside the range of `int32` are converted to `NA`. Future plan is to allow conversion to `double` or use the bit64 package.
`half` / `float16` | ✔ / ❌ | Converted to `double` in R. No effort is made to assess loss of precision due to conversion.
`single` / `float32` | ✔ / ✔ | Converted to `double` in R. No effort is made to assess loss of precision due to conversion.
`double` / `float64` | ✔ / ✔ |
`complex` | ❌ / ❌ |
`timedelta` | ❌ / ❌ |
`datetime` | ❌ / ❌ |
`string` | ✔ / ✔ |
`Unicode` | ✔ / ✔ |
`void *` | ❌ / ❌ |
Structured data types | ❌ / ❌ |

### Codecs

#### Compression codecs

Data Type | Status (reading / writing) | Notes
--- | --- | ---
`zlib / gzip` | ✔ / ✔ | Only system default compression level (normally 6) is enabled for writing.
`bzip2` | ✔ / ✔ | Only compression level 9 is enabled for writing.
`blosc` | ✔ / ✔ | Only `lz4` compression level 5 is enabled for writing.
`LZMA` | ✔ / ✔ |
`LZ4` | ✔ / ✔ |
`Zstd` | ✔ / ✔ |

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

#### Other codecs

Codec | Status (reading / writing) | Notes
--- | --- | ---
`endian` | ✔ / ❌ |
`transpose` | ✔ / ✔ | Only the simple T/C case defined in v2