IoTDB-Quality

# Re_sample

# Usage

This function is used to resample the input series according to a given frequency, including up-sampling and down-sampling. Currently, the supported up-sampling methods are NaN (filling with NaN), FFill (filling with previous value), BFill (filling with next value) and Linear (filling with linear interpolation). Down-sampling relies on group aggregation, which supports Max, Min, First, Last, Mean and Median.

Name: RE_SAMPLE

Input Series: Only support a single input series. The type is INT32 / INT64 / FLOAT / DOUBLE.

Parameters:

  • every: The frequency of resampling, which is a positive number with an unit. The unit is 'ms' for millisecond, 's' for second, 'm' for minute, 'h' for hour and 'd' for day. This parameter cannot be lacked.
  • interp: The interpolation method of up-sampling, which is 'NaN', 'FFill', 'BFill' or 'Linear'. By default, NaN is used.
  • aggr: The aggregation method of down-sampling, which is 'Max', 'Min', 'First', 'Last', 'Mean' or 'Median'. By default, Mean is used.
  • start: The start time (inclusive) of resampling with the format 'yyyy-MM-dd HH:mm:ss'. By default, it is the timestamp of the first valid data point.
  • end: The end time (exclusive) of resampling with the format 'yyyy-MM-dd HH:mm:ss'. By default, it is the timestamp of the last valid data point.

Output Series: Output a single series. The type is DOUBLE. It is strictly equispaced with the frequency every.

Note: NaN in the input series will be ignored.

# Examples

# Up-sampling

When the frequency of resampling is higher than the original frequency, up-sampling starts.

Input series:

+-----------------------------+---------------+
|                         Time|root.test.d1.s1|
+-----------------------------+---------------+
|2021-03-06T16:00:00.000+08:00|           3.09|
|2021-03-06T16:15:00.000+08:00|           3.53|
|2021-03-06T16:30:00.000+08:00|            3.5|
|2021-03-06T16:45:00.000+08:00|           3.51|
|2021-03-06T17:00:00.000+08:00|           3.41|
+-----------------------------+---------------+

SQL for query:

select re_sample(s1,'every'='5m','interp'='linear') from root.test.d1

Output series:

+-----------------------------+-----------------------------------------------------------+
|                         Time|re_sample(root.test.d1.s1, "every"="5m", "interp"="linear")|
+-----------------------------+-----------------------------------------------------------+
|2021-03-06T16:00:00.000+08:00|                                         3.0899999141693115|
|2021-03-06T16:05:00.000+08:00|                                         3.2366665999094644|
|2021-03-06T16:10:00.000+08:00|                                         3.3833332856496177|
|2021-03-06T16:15:00.000+08:00|                                         3.5299999713897705|
|2021-03-06T16:20:00.000+08:00|                                         3.5199999809265137|
|2021-03-06T16:25:00.000+08:00|                                          3.509999990463257|
|2021-03-06T16:30:00.000+08:00|                                                        3.5|
|2021-03-06T16:35:00.000+08:00|                                          3.503333330154419|
|2021-03-06T16:40:00.000+08:00|                                          3.506666660308838|
|2021-03-06T16:45:00.000+08:00|                                          3.509999990463257|
|2021-03-06T16:50:00.000+08:00|                                         3.4766666889190674|
|2021-03-06T16:55:00.000+08:00|                                          3.443333387374878|
|2021-03-06T17:00:00.000+08:00|                                         3.4100000858306885|
+-----------------------------+-----------------------------------------------------------+

# Down-sampling

When the frequency of resampling is lower than the original frequency, down-sampling starts.

Input series is the same as above, the SQL for query is shown below:

select re_sample(s1,'every'='30m','aggr'='first') from root.test.d1

Output series:

+-----------------------------+---------------------------------------------------------+
|                         Time|re_sample(root.test.d1.s1, "every"="30m", "aggr"="first")|
+-----------------------------+---------------------------------------------------------+
|2021-03-06T16:00:00.000+08:00|                                       3.0899999141693115|
|2021-03-06T16:30:00.000+08:00|                                                      3.5|
|2021-03-06T17:00:00.000+08:00|                                       3.4100000858306885|
+-----------------------------+---------------------------------------------------------+

# Specify the time period

The time period of resampling can be specified with start and end. The period outside the actual time range will be interpolated.

Input series is the same as above, the SQL for query is shown below:

select re_sample(s1,'every'='30m','start'='2021-03-06 15:00:00') from root.test.d1

Output series:

+-----------------------------+------------------------------------------------------------------------+
|                         Time|re_sample(root.test.d1.s1, "every"="30m", "start"="2021-03-06 15:00:00")|
+-----------------------------+------------------------------------------------------------------------+
|2021-03-06T15:00:00.000+08:00|                                                                     NaN|
|2021-03-06T15:30:00.000+08:00|                                                                     NaN|
|2021-03-06T16:00:00.000+08:00|                                                       3.309999942779541|
|2021-03-06T16:30:00.000+08:00|                                                      3.5049999952316284|
|2021-03-06T17:00:00.000+08:00|                                                      3.4100000858306885|
+-----------------------------+------------------------------------------------------------------------+

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