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Convert m-Path timestamps to a date time format

Source: R/timestamps_to_datetime.R
timestamps_to_datetime.Rd

[Stable]

m-Path timestamps are based on the participant's local time zone, and when converted to R datetime format, they are interpreted as being in Coordinated Universal Time (UTC), previously known Greenwich Mean Time (GMT). This function allows for the conversion of m-Path timestamps to datetime, and optionally allows for the specification of a UTC offset or a forced time zone.

Usage

timestamps_to_datetime(x, tz_offset = NULL, force_tz = NULL)

Arguments

x

A vector of timestamps to be transformed to datetime.

tz_offset

A numeric value to be added to the timestamps before transforming to datetime. This is typically derived from the timeZoneOffset column from m-Path data. This is only useful when you want to compare timestamps in an absolute manner or link it to external data sources.

force_tz

A string specifying the time zone to force the timestamps to. This is useful when the data is to be compared to other data sources that are in a different time zone. Note that this will not change the actual time of the timestamp, but only the time zone that is displayed. A list of time zones can be used in OlsonNames().

Value

A vector of POSIXct objects representing the timestamps in the UTC time zone. The time zone may differ if force_tz is specified.

Details

This function has three use cases:

  1. The most common use case: You have only ESM data and want to work in each participant's local time zone. In this case, the tz_offset and force_tz should be left empty. This is likely the right use case for you.

  2. You have ESM data and external data (e.g. sensing data or data from a multi-lab study) that you want to match based on their time stamp. The external data is likely in UTC while m-Path data is in the participant's local time zone. In this case, you should specify the tz_offset argument to convert the local time stamps to true UTC time. However, this will change the time stamp to UTC so you will lose the ability to work in the local time zone.

  3. This is a more specialised version of use case 2, namely when you are certain that every participant lives in the same time zone and there not been any changes in daylight savings time. In this case, you can specify the force_tz argument to set the same time zone for all participants. This will not change the displayed time (11AM will stay 11AM) but will change the underlying time zone.

Background

Timestamps in m-Path, like those in timeStampScheduled and timeStampStart, are a variation on UNIX timestamps, defined as the number of seconds since January 1, 1970, at 00:00:00. However, unlike standard UNIX timestamps (which use UTC), m-Path timestamps are based on the participant's local time zone. This is because we are generally interested in time from the participant's perspective and not in an absolute sense compared to other participants. Unfortunately, having multiple time zones in a single column is a not possible in R, which is why all time zones are (incorrectly) displayed as UTC.

When converted to R datetime format, they may display as UTC, which could lead to confusion. This typically isn't an issue when analyzing ESM data within the participant's local context, but it can affect comparisons with other data sources. For accurate cross-referencing with other data, consider specifying the UTC offset to correctly adjust for the participant’s local time. Alternatively, you can force the timestamps to display in a specific time zone using the force_tz argument.

Examples

data <- read_mpath(
  mpath_example("example_basic.csv"),
  mpath_example("example_meta.csv")
)[1:10,]

# The most common use case for this function: Convert
# `timeStampStart` to datetime. Remember that these are in the
# local time zone, but R displays them as being in UTC.
timestamps_to_datetime(data$timeStampStart)
#>  [1] "2024-04-18 09:55:42 UTC" "2024-04-19 08:16:42 UTC"
#>  [3] "2024-04-19 09:00:31 UTC" "2024-04-19 15:24:27 UTC"
#>  [5] "2024-04-19 17:20:04 UTC" "2024-04-19 20:08:40 UTC"
#>  [7] "2024-04-19 21:48:08 UTC" "2024-04-19 22:15:22 UTC"
#>  [9] "2024-04-20 09:32:02 UTC" "2024-04-20 11:26:45 UTC"

# Convert `timeStampStop` to datetime, but as being the correct
# value in UTC.
timestamps_to_datetime(
  x = data$timeStampStop,
  tz_offset = data$timeZoneOffset
)
#>  [1] "2024-04-18 07:57:30 UTC" "2024-04-19 06:17:54 UTC"
#>  [3] "2024-04-19 07:01:08 UTC" "2024-04-19 13:25:11 UTC"
#>  [5] "2024-04-19 15:20:50 UTC" "2024-04-19 18:09:27 UTC"
#>  [7] "2024-04-19 19:48:31 UTC" "2024-04-19 20:16:08 UTC"
#>  [9] "2024-04-20 07:32:35 UTC" "2024-04-20 09:27:11 UTC"

# Let's convert `timeStampSent` to datetime, but this time we want to
# force the time zone to be in "America/New_York" as we know all
# participants were in this time zone and so we can link with other
# data that is also in New York's time zone.
timestamps_to_datetime(
  x = data$timeStampSent,
  force_tz = "America/New_York"
)
#>  [1] "2024-04-18 09:55:41 EDT" "2024-04-19 08:16:36 EDT"
#>  [3] "2024-04-19 09:00:28 EDT" "2024-04-19 15:02:56 EDT"
#>  [5] "2024-04-19 17:17:57 EDT" "2024-04-19 19:44:27 EDT"
#>  [7] "2024-04-19 21:23:23 EDT" "2024-04-19 22:10:01 EDT"
#>  [9] "2024-04-20 09:03:24 EDT" "2024-04-20 11:26:28 EDT"