The $trend tag can take an optional time_delta parameter. $trend($time_delta=604800).outTemp
would return the difference in temperature from exactly one week ago. Mind you, this is not a difference from an average temperature or anything. Just a straight difference between two records exactly a week apart. If you want to do some averaging, then you'll have to define your own search list extension to provide something like: $diff($time_delta=604800, $aggregation_time=86400).outTemp -tk On Tue, Nov 28, 2017 at 5:45 PM, Michael Hornsby < [email protected]> wrote: > Thanks Tom > > I though you could only have one time delta for a trend ? So if I did week > and could not have month or year ? > > Cheers > Michael > > On Wednesday, 29 November 2017 10:40:51 UTC+11, Tom Keffer wrote: >> >> Hello, Michael and welcome to WeeWX. >> >> Would it work if I did something like >>> seven_day_stats1 = TimespanBinder .... >>> seven_day_stats2 = TimespanBinder .... >>> seven_day_stats = seven_day_stats1 - seven_day_stats2 >> >> >> Unfortunately, no, because there is no subtraction operator defined for >> type TimespanBinder. >> >> Why not just use the existing tag $trend >> <http://weewx.com/docs/customizing.htm#_________Tag_$trend_______>? If >> that's not what you had in mind, try hacking object TrendObj to get exactly >> what you want. >> >> -tk >> >> >> On Tue, Nov 28, 2017 at 5:17 PM, Michael Hornsby <[email protected]> >> wrote: >> >>> Hi >>> >>> I'm migrating from wview and very excited with what can be done with >>> weewx. At the moment I have php code and custom C code and I can see I can >>> create a much better package with weewx. >>> >>> I'm trying to get my head around how a can construct a search list >>> extension so I can find the change in a value from a week , month or year >>> ago >>> >>> For example in a template I have this >>> $week.outHumidity.avg.raw - $week($weeks_ago=1).outHumidity.avg.raw >>> >>> I want to know compared to last week / month / year whats the difference >>> in the average temp , total rain etc >>> >>> I'm looking at the example below and thinking ok. So I need to run the >>> stats for two periods and subtract them. >>> >>> >>> week_dt = datetime.date.fromtimestamp(timespan.stop) - \ >>> >>> datetime.timedelta(weeks=1) >>> # 5 >>> # Convert it to unix epoch time: >>> week_ts = time.mktime(week_dt.timetuple()) >>> # 6 >>> # Form a TimespanBinder object, using the time span we just >>> # calculated: >>> seven_day_stats = TimespanBinder(TimeSpan(week_ts, timespan.stop), >>> db_lookup, >>> formatter=self.generator.formatter, >>> converter=self.generator.converter, >>> skin_dict=self.generator.skin_dict) >>> >>> >>> >>> Would it work if I did something like >>> >>> seven_day_stats1 = TimespanBinder .... >>> seven_day_stats2 = TimespanBinder .... >>> >>> seven_day_stats = seven_day_stats1 - seven_day_stats2 >>> >>> >>> Thanks - I contributed a few features to wview. Hopefully I can do the >>> same with weewx. >>> >>> Cheers >>> Michael >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "weewx-user" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- > You received this message because you are subscribed to the Google Groups > "weewx-user" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
