hasdata

R2026b

Determine whether data is available to read

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Syntax

tf = hasdata(dst)

Description

tf = hasdata(dst) returns logical 1 if the datastore object dst has data available to read. When dst does not have data available to read, hasdata returns 0.

example

Examples

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Open Live Script

You can log big data from a simulation and inspect and analyze portions of that data by interacting with a matlab.io.datastore.SimulationDatastore object. This example is meant as a demonstration and does not log big data.

Log Big Data from Model

Open the model ThreeSigs.

mdl = "ThreeSigs";
open_system(mdl)

To log data to persistent storage, select Configuration Parameters > Data Import/Export > Log data to file. Alternatively, you can log data in Dataset format to a MAT file instead of the workspace programmatically. 

set_param(mdl,"LoggingToFile","on")

Set the stop time of the simulation to 3000 seconds and simulate the model.

set_param(mdl,StopTime="3000")
out = sim(mdl);

The MAT file out.mat appears in your current folder. The software stores logged output data in the MAT file with the variable name yout.

Create a DatasetRef object that refers to the logged signal data.

DSRef = Simulink.SimulationData.DatasetRef("out.mat","yout");

Preview Big Data

To return a SimulationDatastore representation of the sineSig signal, which is the first element in the DatasetRef object DSRef, use curly braces. The SimulationDatastore object exists in the Values property of the returned Signal object.

SimDataSig = DSRef{1};
DStore = SimDataSig.Values;

To inspect the first ten samples of logged sineSig data, use preview.

preview(DStore)
ans = 10×1 timetable
     Time        Data  
    _______    ________

    0 sec             0
    0.1 sec    0.099833
    0.2 sec     0.19867
    0.3 sec     0.29552
    0.4 sec     0.38942
    0.5 sec     0.47943
    0.6 sec     0.56464
    0.7 sec     0.64422
    0.8 sec     0.71736
    0.9 sec     0.78333

Inspect Specific Sample

Suppose you want to inspect the 603rd sample of logged sineSig data. Set the ReadSize property of DStore to a number that, considering memory resources, your computer can tolerate. For example, set ReadSize to 200.

DStore.ReadSize = 200;

Read from the datastore three times. Each read operation advances the reading position by 200 samples.

read(DStore);
read(DStore);
read(DStore);

Now that you are close to the 603rd sample, you can set ReadSize to a smaller number to make the target sample easier to find. For example, set ReadSize to 5.

DStore.ReadSize = 5;

Read from the datastore again. The third sample of read data is the 603rd sample in the datastore.

read(DStore)
ans = 5×1 timetable
      Time        Data  
    ________    ________

    60 sec      -0.30481
    60.1 sec    -0.39837
    60.2 sec    -0.48795
    60.3 sec    -0.57265
    60.4 sec    -0.65164

Inspect Earlier Sample

To inspect an earlier sample, reset the datastore to start reading from the first sample. For example, inspect the 403rd sample of logged sinSig data. Due to previous read operations, the datastore now reads starting from the 606th sample.

To read DStore from the beginning, use reset. Then, set ReadSize to 200 and read from the datastore twice to advance the read position to the 401st sample.

reset(DStore);
DStore.ReadSize = 200;

read(DStore);
read(DStore);

Set ReadSize to 5 and read from the datastore. Now, the third sample of read data is the 403rd sample in the datastore.

DStore.ReadSize = 5;
read(DStore)
ans = 5×1 timetable
      Time       Data  
    ________    _______

    40 sec      0.74511
    40.1 sec    0.67481
    40.2 sec    0.59776
    40.3 sec    0.51474
    40.4 sec    0.42658

Extract Multiple Samples

You can also use the read function to extract multiple samples. For example, extract samples 1001 through 1020.

Reset the datastore. Then, advance to sample 1001 by setting the ReadSize property to 200 and reading the datastore five times.

reset(DStore)

DStore.ReadSize = 200;
for i = 1:5
    read(DStore);
end

Set the ReadSize to 20 to extract 20 samples from the datastore.

DStore.ReadSize = 20;

Extract samples 1001 through 1020. Store the extracted data in a variable named targetSamples.

targetSamples = read(DStore)
targetSamples = 20×1 timetable
      Time         Data  
    _________    ________

    100 sec      -0.50637
    100.1 sec    -0.41775
    100.2 sec    -0.32496
    100.3 sec    -0.22892
    100.4 sec    -0.13059
    100.5 sec    -0.03096
    100.6 sec     0.06898
    100.7 sec     0.16823
    100.8 sec      0.2658
    100.9 sec     0.36072
    101 sec       0.45203
    101.1 sec     0.53882
    101.2 sec     0.62023
    101.3 sec     0.69544
    101.4 sec     0.76371
    101.5 sec     0.82434
      ⋮

Find Maximum Value of Data in Datastore

Use the hasdata function as the condition for a while loop to incrementally analyze the data in chunks of 200 samples.

reset(DStore);
DStore.ReadSize = 200;
runningMax = [];
while hasdata(DStore)
    tt = read(DStore);
    rawChunk = tt.Data;
    runningMax = max([rawChunk; runningMax]);
end

The variable runningMax stores the maximum value in the entire datastore.

runningMax
runningMax = 
1.0000
Open Live Script

A matlab.io.datastore.sdidatastore object references signal data in the Simulation Data Inspector repository. When the signal is too large to fit into memory, you can use the sdidatastore object to incrementally process the data manually or to create a tall timetable for the signal that handles the incremental processing for you.

Create sdidatastore for Signal

Simulate the ThreeSigs model, which is configured to log three signals, to create data in the Simulation Data Inspector repository.

mdl = "ThreeSigs";
out = sim(mdl);

The model is configured to log data using a single Simulink.SimulationOutput object named out. The SimulationOutput object contains the logged output data in a Simulink.SimulationData.Dataset object named yout. Use dot notation to access the logged data. 

out.yout
ans = 
Simulink.SimulationData.Dataset 'yout' with 3 elements

                         Name      BlockPath      
                         ________  ______________ 
    1  [1x1 Signal]      sineSig   ThreeSigs/Out1
    2  [1x1 Signal]      randSig   ThreeSigs/Out2
    3  [1x1 Signal]      chirpSig  ThreeSigs/Out3

  - Use braces { } to access, modify, or add elements using index.

Get the signal ID for the signal named sineSig.

runCount = Simulink.sdi.getRunCount;
latestRunID = Simulink.sdi.getRunIDByIndex(runCount);
latestRun = Simulink.sdi.getRun(latestRunID);
sineSigID = getSignalIDsByName(latestRun,"sineSig");

Use the signal ID to create an sdidatastore object for the sineSig signal.

sineSDIds = matlab.io.datastore.sdidatastore(sineSigID);

Verify Contents of Datastore

Check the Name property of the sdidatastore object to verify that it matches your expectations.

sineSDIds.Name
ans = 
'sineSig'

You can also use the preview function to verify the first ten samples in the signal.

preview(sineSDIds)
ans = 10×1 timetable
     Time        Data  
    _______    ________

    0 sec             0
    0.1 sec    0.099833
    0.2 sec     0.19867
    0.3 sec     0.29552
    0.4 sec     0.38942
    0.5 sec     0.47943
    0.6 sec     0.56464
    0.7 sec     0.64422
    0.8 sec     0.71736
    0.9 sec     0.78333

Process Signal Data with sdidatastore Object

When your signal is too large to fit into memory, use read to load and incrementally process data from the Simulation Data Inspector repository in chunks. Use hasdata as the condition for a while loop to incrementally process the whole signal. For example, find the maximum signal value.

latestMax = [];

while hasdata(sineSDIds)
    sineChunk = read(sineSDIds);
    sineChunkData = sineChunk.Data;
    latestMax = max([sineChunkData; latestMax]);
end

latestMax
latestMax = 
0.9996

On each read operation, the read function updates the read position for the start of the next read operation. After reading some or all of the sdidatastore object, you can reset the read position to start again from the beginning of the signal.

reset(sineSDIds)

Process Signal Data in Memory

When the signal referenced by your sdidatastore object fits into memory, you can use the readall function to read all the signal data into memory for processing. The readall function returns a timetable with all the signal data.

sineTimetable = readall(sineSDIds);
sineMax = max(sineTimetable.Data)
sineMax = 
0.9996

Input Arguments

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Datastore to check for available data to read, specified as a matlab.io.datastore.sdidatastore, matlab.io.datastore.simulationdatastore object, or matlab.io.datastore.MLDATXSignalDatastore object.

Output Arguments

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Data availability indication, returned as a 1 or 0 of data type logical. When the sdidatastore object has data available to read, tf is 1. When data is not available, tf is 0.

Version History

Introduced in R2017b

See Also

Objects

Functions

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