preview

Preview subset of events from event stream

Since R2022b

This function requires Streaming Data Framework for MATLAB^® Production Server™.

Syntax

tt = preview(stream)

tt = preview(stream,ReadLimit="Time",RequestTimeout=rt)

Description

tt = preview(stream) returns a timetable containing the first eight events from an event stream without advancing the read position. Multiple calls to preview return the same set of events.

example

tt = preview(stream,ReadLimit="Time",RequestTimeout=rt) specifies the request timeout value rt when previewing data in an event stream. This syntax is valid only for KafkaStream objects.

example

Examples

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Preview Event Data

Create an inMemoryStream object to read and write events to an event stream hosted by MATLAB.

is = inMemoryStream;

Write timetable data to the event stream.

load indoors
writetimetable(is,indoors)

Preview the first 8 events in the stream.

preview(is)

ans =

  8×2 timetable

           Time            Humidity    AirQuality
    ___________________    ________    __________

    2015-11-15 00:00:24       36           80    
    2015-11-15 01:13:35       36           80    
    2015-11-15 02:26:47       37           79    
    2015-11-15 03:39:59       37           82    
    2015-11-15 04:53:11       36           80    
    2015-11-15 06:06:23       36           80    
    2015-11-15 07:19:35       36           80    
    2015-11-15 08:32:47       37           80

Set Timeout when Previewing Kafka Event Data

Assume that you have a Kafka^® server running at the network address kafka.host.com:9092 that has a topic IndoorTemp.

Create a KafkaStream object for reading from and writing to the IndoorTemp topic.

ks = kafkaStream("kafka.host.com",9092,"IndoorTemp");

Write timetable data to the event stream.

load indoors
writetimetable(ks,indoors)

Set a timeout value of 30 seconds when previewing the first 8 events.

preview(ks,ReadLimit="Time",RequestTimeout=30)

ans =

  8×2 timetable

           Time            Humidity    AirQuality
    ___________________    ________    __________

    2015-11-15 00:00:24       36           80    
    2015-11-15 01:13:35       36           80    
    2015-11-15 02:26:47       37           79    
    2015-11-15 03:39:59       37           82    
    2015-11-15 04:53:11       36           80    
    2015-11-15 06:06:23       36           80    
    2015-11-15 07:19:35       36           80    
    2015-11-15 08:32:47       37           80

Input Arguments

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`stream` — Object connected to event stream
`KafkaStream` object | `InMemoryStream` object | `TestStream` object

Object connected to an event stream, specified as a KafkaStream, InMemoryStream, or TestStream object.

`rt` — Number of seconds to wait before terminating request
61 (default) | positive integer

Number of seconds to wait before terminating a request that has not yet begun to transfer data, specified as a positive integer.

If the stream provider is Kafka, the wait time includes connecting to the Kafka host as well as data transfer between the Kafka host and the client.

Version History

Introduced in R2022b