Delta transforms

A delta() transform calculates the difference between consecutive values in the timevector. The first point in the timevector is omitted as there is no previous value and it cannot have a delta(). Data should be sorted using the sort() element before passing into delta(). For example:

SELECT (
    toolkit_experimental.timevector(time, value)
    -> toolkit_experimental.sort()
    -> toolkit_experimental.delta()
    -> toolkit_experimental.unnest()).*
FROM (VALUES (TimestampTZ '2021-01-06 UTC',   0.0 ),
             (            '2021-01-01 UTC',  25.0 ),
             (            '2021-01-02 UTC',   0.10),
             (            '2021-01-04 UTC', -10.0 ),
             (            '2021-01-05 UTC',   3.3 )
     ) as v(time, value);

The output for this example:

          time          | value
------------------------+-------
 2021-01-02 00:00:00+00 | -24.9
 2021-01-04 00:00:00+00 | -10.1
 2021-01-05 00:00:00+00 |  13.3
 2021-01-06 00:00:00+00 |  -3.3
(4 rows)

The first row of the output is missing, as there is no way to compute a delta without a previous value.