strptime_eddy: Conversion of Regular Date-time Sequence from Character
In lsigut/openeddy: Post-process eddy covariance data with ease

strptime_eddy

R Documentation

Conversion of Regular Date-time Sequence from Character

Description

Converts character vector to class "POSIXct" using strptime and validates the result. The input has to represent a regular date-time sequence with given time interval. Additional attributes varnames and units are assigned to returned vector with fixed strings "timestamp" and "-", respectively.

Usage

strptime_eddy(
  x,
  format = "%Y-%m-%d %H:%M",
  interval = 1800L,
  shift.by = NULL,
  allow_gaps = FALSE,
  tz = "GMT",
  ...
)

Arguments

`x`	A character vector containing date-time information to be converted to class `"POSIXct"`.
`format`	A character string. The default `format` is `"%Y-%m-%d %H:%M"`
`interval`	A numeric value specifying the time interval (in seconds) of the input date-time vector.
`shift.by`	An integer value specifying the time shift (in seconds) to be applied to the date-time information.
`allow_gaps`	A logical value. If `TRUE`, date-time information does not have to be regular but time differences must be multiples of `interval`.
`tz`	A time zone (see `time zones`) specification to be used for the conversion.
`...`	Further arguments to be passed from or to other methods.

Details

Eddy covariance related measurements are usually stored with a timestamp representing the end of the averaging period (typically 1800 s) in standard time. This can however cause difficulties during data aggregation or plotting. Therefore it is recommended to shift the date-time information using shift.by to represent the center of averaging period prior to any computations. It is also recommended to change the date-time information to its original state before saving to a file (see Examples section).

Any unsuccessful attempt to convert date-time information is considered to be unexpected behavior and returns an error message instead of NA value. In case that multiple formats are present in the timestamp, it has to be corrected prior using strptime_eddy. It is expected that time series are continuous even if no valid measurements are available for given time interval. Therefore interval value is checked against the lagged differences (diff) applied to the converted date-time vector and returns an error message if mismatch is found. If allow_gaps = TRUE, date-time information does not have to be regular but time differences must be multiples of interval.

The storage mode of returned POSIXct vector is forced to be integer instead of double. This simplifies application of round_df but could lead to unexpected behavior if the date-time information is expected to resolve fractional seconds. Similarly as.integer is applied to shift.by before it is added to the POSIXct vector to assure integer storage mode of returned vector.

Examples

xx <- c("01.01.2014  00:30:00", "01.01.2014  01:00:00",
"01.01.2014  01:30:00", "01.01.2014  02:00:00")
varnames(xx) <- "timestamp"
units(xx) <- "-"
str(xx)
(yy <- strptime_eddy(xx, "%d.%m.%Y %H:%M", shift.by = -900L))
attributes(yy)
typeof(yy)

## Convert to original format
format(yy + 900, format = "%d.%m.%Y %H:%M", tz = "GMT")
zz <- xx[-3]
strptime_eddy(zz, "%d.%m.%Y %H:%M", allow_gaps = TRUE)

## Not run: 
## This is not a regular date-time sequence
strptime_eddy(zz, "%d.%m.%Y %H:%M") # error returned
## interval argument provided incorrectly
strptime_eddy(xx, "%d.%m.%Y %H:%M", interval = 3600L)

## End(Not run)

lsigut/openeddy documentation built on Aug. 5, 2023, 12:25 a.m.