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5.1.13 Data Retrieval

Overview

This section describes the data acquisition of time-series container of GridDB in this chapter.


Data Acquisition

The following are methods to fetch and read TimeSeries containers:

Specified time

Time to get the data (= low) of the series container, you will need to specify the time is Rouki of time series container.

List.1 Acquire Data for a Specified Time (TimeSeriesRetrieve.java) 
// Specify Time
InstrumentLog log = logTs.get(format.parse("2016/07/02 12:00"));
System.out.println("get by Time");
System.out.println(String.format("%s\t%-20s\t%-10s", log.timestamp, log.weatherStationId,
		log.temperture));
  • Line 100: Use TimeSeries.get (Date) to get rows with a specified time stamp.

Execution results are as follows.

List.2 Results 
get by Time
Sat Jul 02 12:00:00 EDT 2016 weather_station_1 80.0


Specified range

Time series container will be able to get to specify the range to be retrieved.

List.3 Aquire rows within a Range (TimeSeriesRetrieve.java) 
// Specify Time Range
System.out.println("get by Time Range");
Date start = format.parse("2016/07/02 9:00");
Date end = TimestampUtils.add(start, 6, TimeUnit.HOUR);

Query<InstrumentLog> query = logTs.query(start, end);
// fetch row
RowSet<InstrumentLog> rowSet = query.fetch();
while (rowSet.hasNext()) {
InstrumentLog log = rowSet.next();
System.out.println("Timestamp\t\t\tWeatherStation ID\tTemperture\tLive Image");
System.out.println(String.format("%s\t%-20s\t%-10s\t%s", log.timestamp,
		log.weatherStationId, log.temperture));
}
  • Line 119-120: Generate the start and end time for the range.
  • Line 122: Use TimeSeries.query (Date, Date) method with start and end times for the range of data to fetch.
  • Line 124-126: Fetch rows.

Execution results are as follows.

List.4 Results 
get by Time Range
Sat Jul 02 09:00:00 EDT 2016 weather_station_1 75.0
Sat Jul 02 12:00:00 EDT 2016 weather_station_1 80.0
Sat Jul 02 15:00:00 EDT 2016 weather_station_1 75.0


Relative Time

You can fetch rows with timestamps are earlier or later than specified timestamp with the TimeOperator enum.

Table 1 TimeOperator Enum

Acquisition method Description
TimeOperator.NEXT Returns the oldest among the Rows whose timestamp are identical with or later than the specified time.
TimeOperator.NEXT_ONLY Returns the oldest among the Rows whose timestamp are later than the specified time.
TimeOperator.PREVIOUS Returns the newest among the Rows whose timestamp are identical with or earlier than the specified time.
TimeOperator.PREVIOUS_ONLY Returns the newest among the Rows whose timestamp are earlier than the specified time.


Fetching Rows with a Relative Time stamp (TimeSeriesRetrieve.java) 
// Specify the next time, including a specified time
InstrumentLog log = logTs.get(format.parse("2016/07/02 12:00"), TimeOperator.NEXT);
System.out.println("get by Next Time");
System.out.println(String.format("%s\t%-20s\t%-10s", log.timestamp, log.weatherStationId,
		log.temperture));

// Specify the next time
log = logTs.get(format.parse("2016/07/02 12:00"), TimeOperator.NEXT_ONLY);
System.out.println("get by NextOnly Time");
System.out.println(String.format("%s\t%-20s\t%-10s", log.timestamp, log.weatherStationId,
		log.temperture));

// Specify the previous time, including a specified time
log = logTs.get(format.parse("2016/07/02 12:00"), TimeOperator.PREVIOUS);
System.out.println("get by Previous Time");
System.out.println(String.format("%s\t%-20s\t%-10s", log.timestamp, log.weatherStationId,
		log.temperture));

// Specify the previous time
log = logTs.get(format.parse("2016/07/02 12:00"), TimeOperator.PREVIOUS_ONLY);
System.out.println("get by PreviousOnly Time");
System.out.println(String.format("%s\t%-20s\t%-10s", log.timestamp, log.weatherStationId,
		log.temperture));
  • Line 144: you get to specify the TimeOperator.NEXT.
  • Line 150: you get to specify the TimeOperator.NEXT_ONLY.
  • Line 156: you get to specify the TimeOperator.PREVIOUS.
  • Line 162: you get to specify the TimeOperator.PREVIOUS_ONLY.

Serving as a reference time has designated all " 2016/07/02 12:00 ".

Execution results are as follows.

List.6 Results that the constant time was on the basis of 
get by Next Time
Sat Jul 02 12:00:00 EDT 2016 weather_station_1 80.0
get by NextOnly Time
Sat Jul 02 15:00:00 EDT 2016 weather_station_1 75.0
get by Previous Time
Sat Jul 02 12:00:00 EDT 2016 weather_station_1 80.0
get by PreviousOnly Time
Sat Jul 02 09:00:00 EDT 2016 weather_station_1 75.0


Aggregatation

Time series container is able to aggregate the data for the specified time period.

List.7 Aggregate Average 
// Average Temperature
Date start = format.parse("2016/07/01 12:00");
Date end = format.parse("2016/07/02 9:00");
AggregationResult aggrResult =
		logTs.aggregate(start, end, "temperture", Aggregation.AVERAGE);
System.out.println("Average Temperature:" + aggrResult.getDouble() + "\n");
  • 181-182 line: TimeSeries.aggregate (Date, Date, String, Aggregation) method You have a summary to find the average value of the temperature.

Execution results are as follows.

List.8 Aggregate Results 
Average Temperature: 67.5

The different types of Aggregation methods are as follows:

Table 2 Aggregation types

Aggregation method Description
Aggregation.AVERAGE Obtain the average value.
Aggregation.COUNT Obtain the number of samples.
Aggregation.MAXIMUM Obtain the maximum value.
Aggregation.MINIMUM Obtain the minimum value.
Aggregation.STANDARD_DEVIATION Obtain the standard deviation.
Aggregation.TOTAL Obtain the total value (sum).
Aggregation.VARIANCE Obtain the variance within the rows.
Aggregation.WEIGHTED_AVERAGE Obtain the weighted average.

For more information, please refer to the GridDB API Reference


Complete source code

Complete source code used in this sample can be downloaded from the following.

Download: timeseries-retrieve.zip