odd time handling in group_times

[robitalec]

group_times can't group odd time thresholds e.g. 2 hour threshold when times are 1am, 3am, 5am... 11pm.

This is because group_times considers the threshold in the context of 24 hours, and a two hour threshold would then group times to 0, 2, 4, 6...

Is there a way around this? Provide an 'offset' argument? Or just make sure it is clear in the vignettes and documentation?

A current workaround is using threshold = '1 hour' which will at least group to 0,1,2,3, ...

[tpodgorski]

this seems to be the problem of the data I'm working with (fixes collected every two hours at uneven hours). Is setting the threshold = '5 minutes' is not enough in this case? If the "sliding window" of 5 minutes starts at midnight and scans the time series, it should capture fixes aggregated both at even and uneven hours, isn't that so? Thanks, Tomasz

[robitalec]

Setting the threshold to '5 minutes' is sufficient when working with fixes collected on uneven hours. (Though see #5 for a recent bug fix).

For example:

DT <- data.table(
  idate = as.IDate('2018-12-12'),
  itime = as.ITime(
    c('01:00', '01:02', '01:01',
      '03:00', '03:02', '03:00',
      '05:00', '05:01', '05:01')
  )
)

group_times(DT, c('idate', 'itime'), threshold = '5 minutes')

idate	itime	minutes	timegroup
2018-12-12	01:00:00	0	1
2018-12-12	01:02:00	0	1
2018-12-12	01:01:00	0	1
2018-12-12	03:00:00	0	2
2018-12-12	03:02:00	0	2
2018-12-12	03:00:00	0	2
2018-12-12	05:00:00	0	3
2018-12-12	05:01:00	0	3
2018-12-12	05:01:00	0	3

This issue is concerned with the (possibly rare?) instance where one might want to group on uneven 2 hour fixes, with a 2 hour threshold. Not sure when one might want this, but right now - it isn't possible.

For example, this data with 2 hour fixes, on the odd hours, with the nearest hour being detected is even.

DT <- data.table(
  idate = as.IDate('2018-12-12'),
  itime = as.ITime(
    c('01:00', '01:02', '00:58',
      '03:00', '03:02', '02:59',
      '05:00', '05:01', '04:58')
  )
)
group_times(DT, c('idate', 'itime'), threshold = '2 hours')

idate	itime	hours	timegroup
2018-12-12	01:00:00	2	1
2018-12-12	01:02:00	2	1
2018-12-12	00:58:00	0	2
2018-12-12	03:00:00	4	3
2018-12-12	03:02:00	4	3
2018-12-12	02:59:00	2	1
2018-12-12	05:00:00	6	4
2018-12-12	05:01:00	6	4
2018-12-12	04:58:00	4	3