subset

Create subset of datastore or file-set

Syntax

subds = subset(ds,indices)

Description

subds = subset(ds,indices)returns a subset containing files corresponding toindices. The subsetsubdsis of the same type as the input.

if the inputdsis a datastore, then the outputoutdsis a datastore of the same type.
if the inputdsis aDsFileSet,FileSet, orBlockedFileSetobject, then the outputsubdsis also, respectively, aDsFileSet,FileSet, orBlockedFileSetobject.

Examples

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Create Subset of`ImageDatastore`

Make an image datastore object and then create a subset of that image datastore.

Create an image datastoreimdsfor all the image files in a sample folder. Then, display theFilesproperty ofimds.

folders = fullfile(matlabroot,'toolbox','matlab',{'demos','imagesci'}); exts = {'.jpg','.png','.tif'}; imds = imageDatastore(folders,'LabelSource','foldernames','FileExtensions',exts); imds.Files

ans = 8×1 cell array {'...\matlab\toolbox\matlab\demos\cloudCombined.jpg'} {'...\matlab\toolbox\matlab\demos\example.tif' } {'...\matlab\toolbox\matlab\demos\landOcean.jpg' } {'...\matlab\toolbox\matlab\demos\ngc6543a.jpg' } {'...\matlab\toolbox\matlab\demos\street1.jpg' } {'...\matlab\toolbox\matlab\demos\street2.jpg' } {'...\matlab\toolbox\matlab\imagesci\corn.tif' } {'...\matlab\toolbox\matlab\imagesci\peppers.png' }

Create a subset datastoresubimds包含第一个四files ofimdsand examine theFilesproperty ofsubimds.

indices = 1:4; subimds = subset(imds,indices); subimds.Files

ans = 4×1 cell array {'...\matlab\toolbox\matlab\demos\cloudCombined.jpg'} {'...\matlab\toolbox\matlab\demos\example.tif' } {'...\matlab\toolbox\matlab\demos\landOcean.jpg' } {'...\matlab\toolbox\matlab\demos\ngc6543a.jpg' }

Create Subset Datastore with Randomly Selected Files

Make an image datastore, and then create subset datastore containing only a specified percentage of files, randomly selected from the original datastore.

CreateimageDatastorefor all the image files in a sample folder and display theFilesproperty. This datastore contains 8 files.

folders = fullfile(matlabroot,'toolbox','matlab',{'demos','imagesci'}); exts = {'.jpg','.png','.tif'}; imds = imageDatastore(folders,'LabelSource','foldernames','FileExtensions',exts); imds.Files

ans = 8×1 cell array {'...\matlab\toolbox\matlab\demos\cloudCombined.jpg'} {'...\matlab\toolbox\matlab\demos\example.tif' } {'...\matlab\toolbox\matlab\demos\landOcean.jpg' } {'...\matlab\toolbox\matlab\demos\ngc6543a.jpg' } {'...\matlab\toolbox\matlab\demos\street1.jpg' } {'...\matlab\toolbox\matlab\demos\street2.jpg' } {'...\matlab\toolbox\matlab\imagesci\corn.tif' } {'...\matlab\toolbox\matlab\imagesci\peppers.png' }

Create a set of indices that represents randomly selected subset containing60%of the files.

nFiles = length(imds.Files); RandIndices = randperm(nFiles); nSixtyPercent = round(0.6*nFiles); indices = RandIndices(1:nSixtyPercent)

indices = 8 6 4 5 1

Create a subset datastoresubmidsusingindicesand examine itsFilesproperty.

subimds = subset(imds,indices); subimds.Files

ans = 5×1 cell array {'...\matlab\toolbox\matlab\imagesci\peppers.png' } {'...\matlab\toolbox\matlab\demos\street2.jpg' } {'...\matlab\toolbox\matlab\demos\ngc6543a.jpg' } {'...\matlab\toolbox\matlab\demos\street1.jpg' } {'...\matlab\toolbox\matlab\demos\cloudCombined.jpg'}

Input Arguments

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`ds`—Input datastore or file-set
`ImageDatastore`|`DsFileSet`|`FileSet`|`BlockedFileSet`

Input datastore or file-set, specified asImageDatastore,DsFileSet,FileSet,BlockedFileSetobject.

To create anImageDatastoreobject, useimageDatastore.
To create aDsFileSetobject, usematlab.io.datastore.DsFileSet.
To create aFileSetobject, usematlab.io.datastore.FileSet.
To create aBlockedFileSetobject, usematlab.io.datastore.BlockedFileSet.

`indices`—Indices of files to include in subset
vector of indices|logical vector

Indices of files to include in subset, specified as a vector of indices or a logical vector.

The vector of indices must contain the indices of files to include in the subsetsubds.
The logical vector must be of the same length as the number of files in the inputds. Thesubsetmethod creates a subsetsubdscontaining files corresponding to the elements in the logical vector that have a value oftrue.

Elements ofindicesmust be unique.

Data Types:double|logical

Extended Capabilities

Thread-Based Environment
Run code in the background using MATLAB®`backgroundPool`or accelerate code with Parallel Computing Toolbox™`ThreadPool`.

Usage notes and limitations:

在一个线程环境,您可以使用subsetonly with the following datastores:
- ImageDatastoreobjects
- CombinedDatastoreorTransformedDatastoreobjects you create fromImageDatastoreobjects by usingcombineortransform
You can usesubsetwith other datastores if you have Parallel Computing Toolbox™. To do so, run the function using a process-backed parallel pool instead of usingbackgroundPoolorThreadPool(use eitherProcessPoolorClusterPool).

For more information, seeRun MATLAB Functions in Thread-Based Environment.

Version History

Introduced in R2019a