Parsing timestamps in R

lubridate-parsing-timestamps.R

``` r
# Load libraries
library(lubridate)
#> Warning: package 'lubridate' was built under R version 3.6.3
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union
library(dplyr)
#> Warning: package 'dplyr' was built under R version 3.6.3
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union

## strptime handles numerical offsets
strptime("2020-04-06T05:45:00+0300", "%Y-%m-%dT%H:%M:%S%z") %>% as.POSIXct() %>% with_tz("UTC")
#> [1] "2020-04-06 02:45:00 UTC"

## Standard `strptime()` doesn't deal well with an offset that contains colons, even though it is ISO 8601 standard.
## But the strptime() conventions probably predate ISO conventions.
strptime("2020-04-06T05:45:00+03:00", "%Y-%m-%dT%H:%M:%S%z")
#> [1] NA

## Standard `strptime()` can't use %z to parse the 'Z' UTC/Zulu time specifier
strptime("2020-04-06T05:45:00Z", "%Y-%m-%dT%H:%M:%S%z")
#> [1] NA

## But it can use a literal 'Z', but it doesn't understand that it means UTC time.
strptime("2020-04-06T05:45:00Z", "%Y-%m-%dT%H:%M:%SZ")
#> [1] "2020-04-06 05:45:00 CDT"

## You have to tell it explicitly:
strptime("2020-04-06T05:45:00Z", "%Y-%m-%dT%H:%M:%SZ", tz="UTC")
#> [1] "2020-04-06 05:45:00 UTC"



## ... as.POSIXct() has similar limitations



## lubridate::parse_date_time() just works
parse_date_time("2020-04-06T05:45:00+03:00", orders="Ymd HMSz")
#> [1] "2020-04-06 02:45:00 UTC"
parse_date_time("2020-04-06T05:45:00+0300", orders="Ymd HMSz")
#> [1] "2020-04-06 02:45:00 UTC"
parse_date_time("2020-04-06T05:45:00Z", orders="Ymd HMSz")
#> [1] "2020-04-06 05:45:00 UTC"
```

<sup>Created on 2020-10-01 by the [reprex package](https://reprex.tidyverse.org) (v0.3.0)</sup>