# Zarr Python

> Arrays N-dimensionales fragmentados (chunked) para almacenamiento en la nube con Zarr-Python 3: arrays comprimidos, E/S paralela, S3/GCS vía fsspec, compatible con NumPy/Dask/Xarray, para pipelines de computación científica a gran escala.

Fuente: https://skillsagentes.com/skills/k-dense-ai/scientific-agent-skills/zarr-python
Markdown: https://skillsagentes.com/skills/k-dense-ai/scientific-agent-skills/zarr-python.md

Repositorio: https://github.com/K-Dense-AI/scientific-agent-skills
Autor: K-Dense-AI
Licencia: MIT license
Actualizado: el mes pasado
Coste de contexto: 46 tok instalada, 1.9k tok al activarse, 8.4k tok con todos los archivos del bundle
Bundle: 7 archivos, 33 KB
Permisos que pide: read write edit bash

## Instalación

Un skill son archivos markdown: los mismos archivos valen para cualquier agente y lo único que cambia es el directorio de destino, es decir la bandera `--agent`. Añade `-g` para instalarlo en todos los proyectos de la máquina.

```bash
# Claude Code
npx -y skills add K-Dense-AI/scientific-agent-skills --skill zarr-python --agent claude-code
# Cursor
npx -y skills add K-Dense-AI/scientific-agent-skills --skill zarr-python --agent cursor
# Codex
npx -y skills add K-Dense-AI/scientific-agent-skills --skill zarr-python --agent codex
# Gemini CLI
npx -y skills add K-Dense-AI/scientific-agent-skills --skill zarr-python --agent gemini
# Windsurf
npx -y skills add K-Dense-AI/scientific-agent-skills --skill zarr-python --agent windsurf
# Cline
npx -y skills add K-Dense-AI/scientific-agent-skills --skill zarr-python --agent cline
```

## Qué hace

- Crea y gestiona arrays N-dimensionales fragmentados (chunked) y comprimidos con `zarr.create_array`, `zarr.zeros`, `zarr.ones`, `zarr.full` y `zarr.array`
- Organiza arrays en grupos jerárquicos, similares a directorios o HDF5, con `create_group`, `require_group`, `create_array` y `require_array`
- Permite indexado estilo NumPy, incluido indexado avanzado (`vindex`, `oindex`, `blocks`), redimensionar (`resize`) y añadir datos (`append`)
- Adjunta metadatos JSON-serializables a arrays y grupos vía `.attrs`
- Cubre almacenamiento local, en memoria, ZIP y remoto (S3, GCS vía fsspec) y la integración con NumPy, Dask y Xarray

## Cuándo usarla

- Almacenar arrays N-dimensionales grandes con chunking y compresión
- Necesitar E/S paralela o flujos de trabajo cloud-native (S3, GCS)
- Integrar arrays con NumPy, Dask o Xarray en pipelines de computación científica a gran escala

## Qué la activa

- "Crea un array Zarr 2D con chunks de 1000x1000"
- "Organiza estos arrays en grupos jerárquicos con Zarr"
- "Guarda este array grande en S3 con Zarr"
- "Migra este código de Zarr v2 a v3"

## Antes de instalar

- Necesita Python 3.12+ y zarr 3.x; la E/S en la nube requiere `zarr[remote]` más s3fs o gcsfs con versión fijada, y los flujos Zarr v2 heredados necesitan Python más antiguo con zarr 2.x fijado.

## Archivos

- SKILL.md — 7 KB
- references/api_reference.md — 5 KB
- references/chunking_and_compression.md — 4 KB
- references/integration.md — 4 KB
- references/performance_and_patterns.md — 5 KB
- references/storage_backends.md — 3 KB
- references/v3_migration.md — 5 KB

## SKILL.md

Reproducido tal cual desde K-Dense-AI/scientific-agent-skills bajo MIT license. Esta sección es el documento original y está en inglés.

# Zarr Python

## Overview

Zarr is a Python library for storing large N-dimensional arrays with chunking and compression. Apply this skill for efficient parallel I/O, cloud-native workflows, and seamless integration with NumPy, Dask, and Xarray.

**Current upstream:** zarr **3.2.1** (released 2026-05-05). Docs: [zarr.readthedocs.io](https://zarr.readthedocs.io/en/stable/). New arrays default to **Zarr format 3**; set `zarr_format=2` for legacy interop. Zarr 3.2 adds rectilinear chunks and continues to refine the v3 codec pipeline. This skill is a **community guide** maintained by K-Dense Inc., not an official zarr-developers package.

## Quick Start

### Installation

```bash
uv pip install "zarr==3.2.1"
```

Requires **Python 3.12+** and NumPy 2.0+ for current stable Zarr-Python. For remote stores (S3, GCS, HTTP), pin the optional extras/backends in your project lockfile:

```bash
uv pip install "zarr[remote]==3.2.1" "s3fs==2026.4.0" "gcsfs==2026.5.0"
```

Use a version range such as `zarr>=3,<4` only when your project has a committed lockfile and compatibility tests. For Zarr-Python 2 / Python 3.10–3.11 workflows, choose an exact `zarr==2.x.y` patch version from the support-v2 release notes and commit the resulting lockfile.

### Basic Array Creation

```python
import zarr
import numpy as np

# Create a 2D array with chunking and compression
z = zarr.create_array(
    store="data/my_array.zarr",
    shape=(10000, 10000),
    chunks=(1000, 1000),
    dtype="f4"
)

# Write data using NumPy-style indexing
z[:, :] = np.random.random((10000, 10000))

# Read data
data = z[0:100, 0:100]  # Returns NumPy array
```

## Core Operations

### Creating Arrays

Zarr provides multiple convenience functions for array creation:

```python
# Create empty array
z = zarr.zeros(shape=(10000, 10000), chunks=(1000, 1000), dtype='f4',
               store='data.zarr')

# Create filled arrays
z = zarr.ones((5000, 5000), chunks=(500, 500))
z = zarr.full((1000, 1000), fill_value=42, chunks=(100, 100))

# Create from existing data
data = np.arange(10000).reshape(100, 100)
z = zarr.array(data, chunks=(10, 10), store='data.zarr')

# Create like another array
z2 = zarr.zeros_like(z)  # Matches shape, chunks, dtype of z
```

### Opening Existing Arrays

```python
# Open array (read/write mode by default)
z = zarr.open_array('data.zarr', mode='r+')

# Read-only mode
z = zarr.open_array('data.zarr', mode='r')

# The open() function auto-detects arrays vs groups
z = zarr.open('data.zarr')  # Returns Array or Group
```

### Reading and Writing Data

Zarr arrays support NumPy-like indexing:

```python
# Write entire array
z[:] = 42

# Write slices
z[0, :] = np.arange(100)
z[10:20, 50:60] = np.random.random((10, 10))

# Read data (returns NumPy array)
data = z[0:100, 0:100]
row = z[5, :]

# Advanced indexing
z.vindex[[0, 5, 10], [2, 8, 15]]  # Coordinate indexing
z.oindex[0:10, [5, 10, 15]]       # Orthogonal indexing
z.blocks[0, 0]                     # Block/chunk indexing
```

### Resizing and Appending

```python
# Resize array (v3: pass shape as a tuple)
z.resize((15000, 15000))

# Append data along an axis
z.append(np.random.random((1000, 10000)), axis=0)  # Adds rows
```

## Groups and Hierarchies

Groups organize multiple arrays hierarchically, similar to directories or HDF5 groups.

### Creating and Using Groups

```python
# Create root group
root = zarr.group(store='data/hierarchy.zarr')

# Create sub-groups
temperature = root.create_group('temperature')
precipitation = root.create_group('precipitation')

# Create arrays within groups
temp_array = temperature.create_array(
    name='t2m',
    shape=(365, 720, 1440),
    chunks=(1, 720, 1440),
    dtype='f4'
)

precip_array = precipitation.create_array(
    name='prcp',
    shape=(365, 720, 1440),
    chunks=(1, 720, 1440),
    dtype='f4'
)

# Access using paths
array = root['temperature/t2m']

# Visualize hierarchy
print(root.tree())
# Output:
# /
#  ├── temperature
#  │   └── t2m (365, 720, 1440) f4
#  └── precipitation
#      └── prcp (365, 720, 1440) f4
```

### Group API (v3)

Use `create_array` / `require_array` (h5py-style `create_dataset` / `require_dataset` were removed in v3):

```python
root = zarr.group('data.zarr')
arr = root.create_array('my_data', shape=(1000, 1000), chunks=(100, 100), dtype='f4')

grp = root.require_group('subgroup')
arr2 = grp.require_array('array', shape=(500, 500), chunks=(50, 50), dtype='i4')
```

## Attributes and Metadata

Attach custom metadata to arrays and groups using attributes:

```python
# Add attributes to array
z = zarr.zeros((1000, 1000), chunks=(100, 100))
z.attrs['description'] = 'Temperature data in Kelvin'
z.attrs['units'] = 'K'
z.attrs['created'] = '2024-01-15'
z.attrs['processing_version'] = 2.1

# Attributes are stored as JSON
print(z.attrs['units'])  # Output: K

# Add attributes to groups
root = zarr.group('data.zarr')
root.attrs['project'] = 'Climate Analysis'
root.attrs['institution'] = 'Research Institute'

# Attributes persist with the array/group
z2 = zarr.open('data.zarr')
print(z2.attrs['description'])
```

**Important**: Attributes must be JSON-serializable (strings, numbers, lists, dicts, booleans, null).

## Chunking, Compression, Storage, and Performance

- [references/chunking_and_compression.md](references/chunking_and_compression.md):
  sizing chunks to the access pattern (aim for ~1 MB, 5-100 MB on cloud), sharding, and
  codec choice.
- [references/storage_backends.md](references/storage_backends.md): local, memory, ZIP,
  and fsspec remote stores (S3, GCS), with credential guidance — prefer IAM roles or
  workload identity, and never print credential values.
- [references/integration.md](references/integration.md): NumPy, Dask, and Xarray
  integration, thread safety, and consolidated metadata.
- [references/performance_and_patterns.md](references/performance_and_patterns.md):
  optimization, appendable time-series and large-matrix patterns, format conversion, and
  troubleshooting.
- [references/api_reference.md](references/api_reference.md) and
  [references/v3_migration.md](references/v3_migration.md): full API and the v2-to-v3
  migration notes.

## Additional Resources

### Bundled references

| File | Contents |
|------|----------|
| `references/api_reference.md` | Function signatures, stores, codecs, indexing |
| `references/v3_migration.md` | Zarr-Python 2→3 breaking changes and WIP features |

### Official upstream

- **Documentation**: https://zarr.readthedocs.io/en/stable/
- **3.0 migration guide**: https://zarr.readthedocs.io/en/stable/user-guide/v3_migration/
- **Storage backends**: https://zarr.readthedocs.io/en/stable/user-guide/storage/
- **Zarr specifications**: https://zarr-specs.readthedocs.io/
- **GitHub**: https://github.com/zarr-developers/zarr-python
- **Developer chat**: https://ossci.zulipchat.com/#narrow/channel/423692-Zarr-Python

**Related libraries:** [Xarray](https://docs.xarray.dev/), [Dask](https://docs.dask.org/), [NumCodecs](https://numcodecs.readthedocs.io/)

## Dónde encaja

- Categoría: [Datos y analítica](https://skillsagentes.com/categorias/datos-analitica.md) — Consulta, limpia y visualiza datos sin salir del agente.
- Creador: [K-Dense-AI](https://skillsagentes.com/creators/k-dense-ai.md) — 163 skills en el directorio
- [Todas las skills](https://skillsagentes.com/skills.md)
- [Ranking de instalaciones](https://skillsagentes.com/ranking.md)

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