In-memory Zarr Store

This class implements a Zarr store in RAM memory. With this class Zarr stores can be read and written to. Obviously, any data is not persisted after the memory store is de-referenced and garbage-collected.

All data is stored in a list. The Zarr array itself has a list with the metadata, its chunks have names like "c.0.0.0" and they have an R array-like value.

This class performs no sanity checks on any of the arguments passed to the methods, for performance reasons. Since this class should be accessed through group and array objects, it is up to that code to ensure that arguments are valid, in particular keys and prefixes.

Super class

zarr::zarr_store -> zarr_memorystore

Active bindings

friendlyClassName

(read-only) Name of the class for printing.

separator

(read-only) The separator of the memory store, always a dot '.'.

keys

(read-only) The defined keys in the store.

Methods

Public methods

• zarr_memorystore$new()

• zarr_memorystore$exists()

• zarr_memorystore$clear()

• zarr_memorystore$erase()

• zarr_memorystore$erase_prefix()

• zarr_memorystore$list_dir()

• zarr_memorystore$list_prefix()

• zarr_memorystore$set()

• zarr_memorystore$set_if_not_exists()

• zarr_memorystore$get()

• zarr_memorystore$get_metadata()

• zarr_memorystore$create_group()

• zarr_memorystore$create_array()

Inherited methods

• zarr::zarr_store$getsize()
• zarr::zarr_store$getsize_prefix()
• zarr::zarr_store$is_empty()
• zarr::zarr_store$list()
• zarr::zarr_store$set_metadata()

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Method new()

Create an instance of this class.

Usage

zarr_memorystore$new()

Returns

An instance of this class.

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Method exists()

Check if a key exists in the store. The key can point to a group, an array (having a metadata list as its value) or a chunk.

Usage

zarr_memorystore$exists(key)

Arguments

key

Character string. The key that the store will be searched for.

Returns

TRUE if argument key is found, FALSE otherwise.

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Method clear()

Clear the store. Remove all keys and values from the store. Invoking this method deletes all data and this action can not be undone.

Usage

zarr_memorystore$clear()

Returns

TRUE. This operation always proceeds successfully once invoked.

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Method erase()

Remove a key from the store. The key must point to an array or a chunk. If the key points to an array, the key and all of subordinated keys are removed.

Usage

zarr_memorystore$erase(key)

Arguments

key

Character string. The key to remove from the store.

Returns

TRUE. This operation always proceeds successfully once invoked, even if argument key does not point to an existing key.

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Method erase_prefix()

Remove all keys in the store that begin with a given prefix.

Usage

zarr_memorystore$erase_prefix(prefix)

Arguments

prefix

Character string. The prefix to groups or arrays to remove from the store, including in child groups.

Returns

TRUE. This operation always proceeds successfully once invoked, even if argument prefix does not point to any existing keys.

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Method list_dir()

Retrieve all keys with a given prefix and which do not contain the character "/" after the given prefix. In other words, this retrieves all the keys in the store below the key indicated by the prefix.

Usage

zarr_memorystore$list_dir(prefix)

Arguments

prefix

Character string. The prefix whose nodes to list.

Returns

A character array with all keys found in the store immediately below the prefix.

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Method list_prefix()

Retrieve all keys and prefixes with a given prefix.

Usage

zarr_memorystore$list_prefix(prefix)

Arguments

prefix

Character string. The prefix to nodes to list.

Returns

A character vector with all paths found in the store below the prefix location.

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Method set()

Store a (key, value) pair. If the value exists, it will be overwritten.

Usage

zarr_memorystore$set(key, value)

Arguments

key

The key whose value to set.

value

The value to set, typically a complete chunk of data, a raw vector.

Returns

Self, invisibly.

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Method set_if_not_exists()

Store a (key, value) pair. If the key exists, nothing will be written.

Usage

zarr_memorystore$set_if_not_exists(key, value)

Arguments

key

The key whose value to set.

value

The value to set, a complete chunk of data.

Returns

Self, invisibly, or an error.

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Method get()

Retrieve the value associated with a given key.

Usage

zarr_memorystore$get(key, prototype = NULL, byte_range = NULL)

Arguments

key

Character string. The key for which to get data.

prototype

Ignored. The only buffer type that is supported maps directly to an R raw vector.

byte_range

If NULL, all data associated with the key is retrieved. If a single positive integer, all bytes starting from a given byte offset to the end of the object are returned. If a single negative integer, the final bytes are returned. If an integer vector of length 2, request a specific range of bytes where the end is exclusive. If the range ends after the end of the object, the entire remainder of the object will be returned. If the given range is zero-length or starts after the end of the object, an error will be returned.

Returns

An raw vector of data, or NULL if no data was found.

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Method get_metadata()

Retrieve the metadata document at the location indicated by the prefix argument.

Usage

zarr_memorystore$get_metadata(prefix)

Arguments

prefix

The prefix whose metadata document to retrieve.

Returns

A list with the metadata, or NULL if the prefix is not pointing to a Zarr array.

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Method create_group()

Create a new group in the store under the specified path.

Usage

zarr_memorystore$create_group(path, name)

Arguments

path

The path to the parent group of the new group. Ignored when creating a root group.

name

The name of the new group. This may be an empty string "" to create a root group. It is an error to supply an empty string if a root group or array already exists.

Returns

A list with the metadata of the group, or an error if the group could not be created.

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Method create_array()

Create a new array in the store under key constructed from the specified path to the parent argument and the name. The key may not already exist in the store.

Usage

zarr_memorystore$create_array(parent, name, metadata)

Arguments

parent

The path to the parent group of the new array. This is ignored if the name argument is the empty string.

name

The name of the new array.

metadata

A list with the metadata for the array. The list has to be valid for array construction. Use the array_builder class to create and or test for validity. An element "chunk_key_encoding" will be added to the metadata if it not already there or contains an invalid separator.

Returns

A list with the metadata of the array, or an error if the array could not be created.