preview
Preview subset of data in datastore
Syntax
Description
Examples
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 = preview(ds)
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 = preview(ds)
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)
Input Arguments
ds
— Input datastore
datastore
Input datastore. You can use these datastores as input to the
preview
method.
MATLAB® datastores — Datastores created using MATLAB
datastore
functions. For example, create a datastore for a collection of images usingImageDatastore
. For a complete list of datastores, see Select Datastore for File Format or Application.Combined and transformed datastores — Datastores created using the
combine
andtransform
functions.Custom datastores — Datastores created using the custom datastore framework. See Develop Custom Datastore.
Output Arguments
data
— Subset of data
table | array
Subset of data, returned as a table or an array depending on the type of
ds
.
Type of Datastore | Data type of data | Description |
---|---|---|
TabularTextDatastore and
SpreadsheetDatastore | Table | Table with variables specified by the
SelectedVariableNames 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:
The |
KeyValueDatastore | Table | Table with the variables Key and
Value . |
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 the
UnderlyingDatastores property. For
example, if the underlying datastore is an image datastore
with a ReadSize property value of 1, then
data 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:
In a thread-based environment, you can use
preview
only with the following datastores:ImageDatastore
objectsCombinedDatastore
,SequentialDatastore
, orTransformedDatastore
objects you create fromImageDatastore
objects by usingcombine
ortransform
You can use
preview
with other datastores if you have Parallel Computing Toolbox™. To do so, run the function using a process-backed parallel pool instead of usingbackgroundPool
orThreadPool
(use eitherProcessPool
orClusterPool
).
For more information, see Run MATLAB Functions in Thread-Based Environment.
Version History
Introduced in R2014b
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