The aggregate function ts.first() returns the oldest value, determined by timecode, for each group.
In the event of a tie, such as simultaneous timecode values for a particular group, all tied results are returned. If a sequence number is present with the data, it can break a tie, assuming it is unique across identical timecode values.
ts.first() uses the argument "value.expression" to specify the column for which oldest value of the group is to be returned.
- This function is valid only on columns with numeric types.
- Nulls are not included in the result computation.
Example 1: Get the oldest value of the 'temperature' column of sequenced PTI table
- Get the oldest value.
> df_seq_first <- df_seq_grp %>% summarise(first_temp = ts.first(temperature))
- Print the results.
> df_seq_first %>% arrange(TIMECODE_RANGE, buoyid, first_temp) # Source: lazy query [?? x 4] # Database: [Teradata 16.20.50.01] [Teradata Native Driver 17.0.0.2] # [TDAPUSER@<hostname>/TDAPUSERDB] # Ordered by: TIMECODE_RANGE, buoyid, first_temp TIMECODE_RANGE `GROUP BY TIME(MINUTES(~ buoyid first_temp <chr> <int64> <int> <int> 1 2014-01-06 08:00:00.000000+00:00,2014-01-06 08:~ 35345 0 10 2 2014-01-06 09:00:00.000000+00:00,2014-01-06 09:~ 35347 1 70 3 2014-01-06 10:00:00.000000+00:00,2014-01-06 10:~ 35349 44 43 4 2014-01-06 10:30:00.000000+00:00,2014-01-06 11:~ 35350 22 23 5 2014-01-06 10:30:00.000000+00:00,2014-01-06 11:~ 35350 44 43 6 2014-01-06 21:00:00.000000+00:00,2014-01-06 21:~ 35371 2 80
Example 2: Get the oldest value of the 'temperature' column of non-PTI table
- Get the oldest value.
> df_nonpti_first <- df_nonpti_grp %>% summarise(first_temp = ts.first(temperature))
- Print the results.
> df_nonpti_first %>% arrange(TIMECODE_RANGE, first_temp) # Source: lazy query [?? x 3] # Database: [Teradata 16.20.50.01] [Teradata Native Driver 17.0.0.2] # [TDAPUSER@<hostname>/TDAPUSERDB] # Ordered by: TIMECODE_RANGE, first_temp TIMECODE_RANGE `GROUP BY TIME(MINUTES(~ first_temp <chr> <int64> <int> 1 2014-01-06 08:00:00.000000+00:00,2014-01-06 08:01:00.~ 23149921 10 2 2014-01-06 08:01:00.000000+00:00,2014-01-06 08:02:00.~ 23149922 10 3 2014-01-06 08:02:00.000000+00:00,2014-01-06 08:03:00.~ 23149923 10 4 2014-01-06 08:03:00.000000+00:00,2014-01-06 08:04:00.~ 23149924 10 5 2014-01-06 08:04:00.000000+00:00,2014-01-06 08:05:00.~ 23149925 10 6 2014-01-06 08:05:00.000000+00:00,2014-01-06 08:06:00.~ 23149926 10 7 2014-01-06 08:06:00.000000+00:00,2014-01-06 08:07:00.~ 23149927 10 8 2014-01-06 08:07:00.000000+00:00,2014-01-06 08:08:00.~ 23149928 10 9 2014-01-06 08:08:00.000000+00:00,2014-01-06 08:09:00.~ 23149929 NA 10 2014-01-06 08:09:00.000000+00:00,2014-01-06 08:10:00.~ 23149930 99 # ... with more rows