How does Last Value mode work when using the Read Timeseries node in Visual Flow Creator?
Solution
When using the Read Timeseries node in Visual Flow Creator, one of the available modes is Last Value. The information reads:
Last value - only one last data point will be read. If the last entry does not include selected variable, the structure will be empty.
To better understand how the mode works and what data is returned, let's use an example where we have two variables, varA and varB with the following timeseries data:
5:00 am - varA = 0, varB = 0
6:00 am - varA = 5, varB = 0
7:00 am - varA = 5, varB = 5
8:00 am - varA = 10, varB = 5
9:00 am - varA = 15, varB = 10
If we read the timeseries data 30 minutes past the hour using Last Value mode, we would get the following data returned:
6:30 am - varA = 5, varB = empty
7:30 am - varA = empty, varB = 5
8:30 am - varA = 10, varB = empty
9:30 am - varA = 15, varB = 10
As you noticed, Last Value mode returns the last time stamped value recorded for the variables selected. For example, at 6:30 am, the last value recorded was for varA. varB did not change and will return empty in this mode because it was not the last value. The next time varB will return data is at 7:30 am and this time, varA will be empty.
When in this mode, the key to remember is that if a variable returns no data, it doesn't mean there is no data, only that it was not the last data point read.
Notes