preview - Preview subset of data in datastore - MATLAB (original) (raw)

Main Content

Preview subset of data in datastore

Syntax

Description

[data](#budueym-1-data) = preview([ds](#budueym-1-ds)) returns a subset of data from datastore ds without changing its current position.

example

Examples

collapse all

Preview Data in TabularTextDatastore

Create a datastore from the sample file, airlinesmall_subset.csv, which contains tabular data.

ds = tabularTextDatastore("airlinesmall_subset.csv","TreatAsMissing","NA",... "MissingValue",0);

Modify the SelectedVariableNames property to specify the variables of interest.

ds.SelectedVariableNames = ["DepTime","ArrTime","ActualElapsedTime"];

Preview the data for the selected variables.

data=8×3 table DepTime ArrTime ActualElapsedTime _______ _______ _________________

 2117       2305             108       
 1252       1511              79       
 1441       1708              87       
 2258       2336              38       
 1814       1901              47       
 1822       1934              72       
  729        841              72       
 1704       1829              85

Preview Data in KeyValueDatastore

Create a datastore from the sample file, mapredout.mat, which is the output file of the mapreduce function.

ds = datastore('mapredout.mat');

Preview the data in the datastore.

data=1×2 table Key Value
______ _________

{'AA'}    {[14930]}

Preview Data in CombinedDatastore

Create a datastore that maintains parity between the pair of images of the underlying datastores. For instance, create two separate image datastores, and then create a combined datastore representing the two underlying datastores.

Create an image datastore imds1 representing a collection of three images.

imds1 = imageDatastore({'street1.jpg','street2.jpg','peppers.png'});

Create a second datastore imds2 by transforming the images of imds1 to grayscale and then reflecting the images horizontally.

imds2 = transform(imds1,@(x) fliplr(im2gray(x)));

Create a combined datastore from imds1 and imds2.

imdsCombined = combine(imds1,imds2);

Preview the data in the combined datastore. The output is a 1-by-2 cell array. The two columns represent the first subset of data from the two underlying datastores imds1 and imds2, respectively.

dataOut = preview(imdsCombined)

dataOut=1×2 cell array {480x640x3 uint8} {480x640 uint8}

Display the previewed data as a pair of tiled images.

tile = imtile(dataOut); imshow(tile)

Figure contains an axes object. The hidden axes object contains an object of type image.

Output Arguments

collapse all

data — Subset of data

table | array

Subset of data, returned as a table or an array depending on the type ofds.

Type of Datastore Data type of data Description
TabularTextDatastore andSpreadsheetDatastore Table Table with variables specified by theSelectedVariableNames property. The table contains at most eight rows.
ImageDatastore Integer array Array of integers corresponding to the first image. The dimensions of the integer array depend on the type of image: For grayscale images,data is m-by-n. For truecolor images,data is m-by-n-by-3. For CMYK Tiff images,data is m-by-n-by-4. The preview function supports all image types supported by theimread function. For more information on the supported image types, see imread.
KeyValueDatastore Table Table with the variables Key andValue.
FileDatastore Table Table containing the output returned by the read function, specified by the 'ReadFcn' parameter in the fileDatastore function.
TransformedDatastore Varies The output is the same as the output returned by the underlying datastore specified by theUnderlyingDatastores property. For example, if the underlying datastore is an image datastore with a ReadSize property value of 1, thendata is returned as an integer array.
CombinedDatastore Cell array Each element of the cell array contains the output returned by the corresponding underlying datastore specified by the UnderlyingDatastores property.
SequentialDatastore Varies The output is a small amount of data from the first nonempty underlying datastore. If all underlying datastores are empty, output is the empty type based on the first underlying datastore. If there are no underlying datastores, output is an empty double.

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:

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

Version History

Introduced in R2014b