SequentialDatastore

Sequentially read data from multiple underlying datastores

Since R2022b

Description

Use a SequentialDatastore object to sequentially read data from multiple datastores without concatenation.

Creation

You can create a SequentialDatastore object using the combine function. For example, dsnew = combine(ds1,ds2,ReadOrder="sequential") creates a datastore that reads data sequentially from datastores ds1 and ds2.

Properties

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`UnderlyingDatastores` — Underlying datastores
cell array

Underlying datastores, specified as a cell array of datastore objects. Resetting the SequentialDatastore object resets all of the underlying datastores.

`SupportedOutputFormats` — Formats supported for writing
string row vector

This property is read-only.

Formats supported for writing, returned as a row vector of strings. This property specifies the possible output formats when using writeall to write output files from the datastore.

Object Functions

`combine`	Combine data from multiple datastores
`hasdata`	Determine if data is available to read
`preview`	Preview subset of data in datastore
`read`	Read data in datastore
`readall`	Read all data in datastore
`writeall`	Write datastore to files
`reset`	Reset datastore to initial state
`transform`	Transform datastore
`numpartitions`	Number of datastore partitions
`partition`	Partition a datastore
`shuffle`	Shuffle all data in datastore
`isPartitionable`	Determine whether datastore is partitionable
`isSubsettable`	Determine whether datastore is subsettable
`isShuffleable`	Determine whether datastore is shuffleable

Examples

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Combine Datastores Sequentially

Open Live Script

Create a datastore that reads from two image datastores one after the other.

Create an ImageDatastore ds1 representing a collection of two images. Then, create a second ImageDatastore ds2 by transforming the images of ds1 to grayscale images. Combine ds1 and ds2 to create a SequentialDatastore object.

ds1 = imageDatastore(["peppers.png","street2.jpg"]); 
ds2 = transform(ds1, @(x) {im2gray(x)});
dsseq = combine(ds1,ds2,ReadOrder="sequential");

Read the first three images from the SequentialDatastore object. Each read operation on this SequentialDatastore object returns a single image represented by a 1-by-1 cell array.

img1 = read(dsseq);
img2 = read(dsseq);
img3 = read(dsseq);

Version History

Introduced in R2022b