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

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

Combine Datastores Sequentially

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