difftime not working

[pratibha]

Hii, I am new to R. I wanted to compute the time difference between two date fields, but I am getting the value as 0.
Here is the formula:
alldata$trip_length <- difftime(alldata$end_time,alldata$start_time)
I am getting trip_length as 0
While doing str(alldata), it is showing as-
$ trip_length : 'difftime' num 0 0 0 0 ...
..- attr(*, "units")= chr "secs"
Can anyone help me in this?

[pratibha]

Hi, I apologize if I didn't make my data clear earlier. I am working on the Google Certification Program Capstone Project. This is how my sample dataset looks like. I need to calculate the trip length which is ended_at-started_at.

#libraries install
library(tidyverse)
library(tidyr)
library(ggplot2)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union

#sample data set
df <- data.frame(
                                                                                                                                                                 stringsAsFactors = FALSE,
                                                                                         NA,
                                                                              started_at = c("1/21/2020 20:06",
                                                                                             "1/30/2020 14:22",
                                                                                             "1/9/2020 19:29",
                                                                                             "1/6/2020 16:17",
                                                                                             "1/30/2020 8:37"),
                                                                                ended_at = c("1/21/2020 20:14",
                                                                                             "1/30/2020 14:26",
                                                                                             "1/9/2020 19:32",
                                                                                             "1/6/2020 16:25",
                                                                                             "1/30/2020 8:42")
)

#There statement is returning 0 secs in trip_length
trip_2021$trip_length <- difftime(trip_2021$ended_at,trip_2021$started_at)
#> Error in as.POSIXct(time1): object 'trip_2021' not found

^{Created on 2021-09-08 by the reprex package (v2.0.1)}

[williaml]

Convert the times to a time format, then use interval:

library(lubridate)
library(tidyverse)

df %>% 
  mutate(started_at = mdy_hm(started_at),
         ended_at = mdy_hm(ended_at)) %>% 
  mutate(difference = interval(started_at, ended_at) / minutes(1))

# A tibble: 5 x 3
  started_at          ended_at            difference
  <dttm>              <dttm>                   <dbl>
1 2020-01-21 20:06:00 2020-01-21 20:14:00          8
2 2020-01-30 14:22:00 2020-01-30 14:26:00          4
3 2020-01-09 19:29:00 2020-01-09 19:32:00          3
4 2020-01-06 16:17:00 2020-01-06 16:25:00          8
5 2020-01-30 08:37:00 2020-01-30 08:42:00          5

[Yarnabrina]

As @williaml has pointed out, you need to convert to date time format first. Then you can use interval, or even difftime as your attempt would work.

trip_2021 <- data.frame(started_at = c("1/21/2020 20:06", "1/30/2020 14:22", "1/9/2020 19:29", "1/6/2020 16:17", "1/30/2020 8:37"),
                        ended_at = c("1/21/2020 20:14", "1/30/2020 14:26", "1/9/2020 19:32", "1/6/2020 16:25", "1/30/2020 8:42"))

within(trip_2021,
       {
           started_at <- as.POSIXct(started_at, format="%m/%d/%Y %H:%M")
    	   ended_at <- as.POSIXct(ended_at, format="%m/%d/%Y %H:%M")
    	   trip_length <- difftime(ended_at, started_at)
       })

Hope this helps.

[pratibha]

It worked, Thank You so much for your support!