as.POSIXct 将时间更改为 NA

Question

When converting time in r using as.POSIXct converts all the values to NA. This is my code to do it:

data1 %>%
mutate(time_clean = ymd_hms(timestamp,tz = 'UTC')) %>%
separate(time_clean, c('date', 'time'), sep = ' ') %>%
mutate_at(vars(date), funs(as.Date))

Sample of the data

data1 <- tribble(
~"time", ~"date",
"07:41:47", "2018-11-08",
"07:41:47", "2018-11-08",
"07:41:47", "2018-11-08",
"07:41:50", "2018-11-08",
"07:41:50", "2018-11-08",
"07:41:50", "2018-11-08")

Answer 1

If you're open to tidyverse solutions, this will accomplish what you need:

library("tidyverse")
# create example data
example_df <- tibble(time = c("07:41:47", "07:41:47", "07:41:50"),
                     date = as.Date(c("2018-11-08", "2018-11-08", "2018-11-08"))) 


example_df %>% 
  unite(col = "datetime",
        c("date", "time"), sep = " ") %>% 
  mutate(datetime = lubridate::ymd_hms(datetime))

But in brief, the issue you're having is related to the fact that as.POSIXct cannot have only a time of the date, without the date. So you need to put date and time in the same string, and then parse it.

If instead you are specifically looking into "time of the day" without date, you may want to check this other question on SO