Date time conversion and extract only time

Question

Want to change the class for Time to POSIXlt and extract only the hours minutes and seconds

str(df3$Time)
chr [1:2075259] \"17:24:00\" \"17:25:00\" \"17:26:0         


        

Answer 1

This is my idiom for getting just the timepart from a datetime object. I use floor_date() from lubridate to get midnight of the timestamp and take the difference of the timestamp and midnight of that day. I create and store a hms object provided with lubridate (I believe) in dataframes because the class has formatting of hh:mm:ss that is easy to read, but the underlying value is a numeric value of seconds. Here is my code:

library(tidyverse)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following object is masked from 'package:base':
#> 
#>     date

# Create timestamps
#
# Get timepart by subtacting the timestamp from it's floor'ed date, make sure
# you convert to seconds, and then cast to a time object provided by the
# `hms` package.
# See: https://www.rdocumentation.org/packages/hms/versions/0.4.2/topics/hms
dt <- tibble(dt=c("2019-02-15T13:15:00", "2019-02-19T01:10:33") %>% ymd_hms()) %>%
  mutate(timepart = hms::hms(as.numeric(dt - floor_date(dt, "1 day"), unit="secs")))

# Look at result
print(dt)
#> # A tibble: 2 x 2
#>   dt                  timepart
#>                   
#> 1 2019-02-15 13:15:00 13:15   
#> 2 2019-02-19 01:10:33 01:10

# `hms` object is really a `difftime` object from documentation, but is made into a `hms`
# object that defaults to always store data in seconds.
dt %>% pluck("timepart") %>% str()
#>  'hms' num [1:2] 13:15:00 01:10:33
#>  - attr(*, "units")= chr "secs"

# Pull off just the timepart column
dt %>% pluck("timepart")
#> 13:15:00
#> 01:10:33

# Get numeric part.  From documentation, `hms` object always stores in seconds.
dt %>% pluck("timepart") %>% as.numeric()
#> [1] 47700  4233

^{Created on 2019-02-15 by the reprex package (v0.2.1)}