Aggregate date time to summarize time spent at certain conditions

Question

I'm stumped with how I should proceed. I have some dummy data below:

 Date <- as.POSIXct(c('2018-03-20 11:52:25', '2018-03-22 12:01:44', '2018-03-20 12:05:25', '2018-03-20 12:10:40', '2018-03-20 12:12:51 ')) 
Sites<-c(4, 4, 4, 6, 7)
Individual<-c("A", "A", "A", "B", "B")

data.frame(Individual, Date, Sites)

Producing this data frame:

  Individual                Date Sites
          A 2018-03-20 11:52:25     4
          A 2018-03-20 12:01:44     4
          A 2018-03-20 12:05:25     4
          B 2018-03-20 12:10:40     6
          B 2018-03-20 12:12:51     7

For each individual, I would like to determine the time spent at each site. Is there a function that will summarize time spent according to the two conditions? Any help or input is much appreciated.

Answer 1

How about this:

library(tidyverse)

Date <- as.POSIXct(c('2018-03-20 11:52:25', '2018-03-22 12:01:44', '2018-03-20 12:05:25', '2018-03-20 12:10:40', '2018-03-20 12:12:51 ')) 
Sites <- c(4, 4, 4, 6, 7)
Individual <- c("A", "A", "A", "B", "B")

df <- data.frame(Individual, Date, Sites)

df %>%
  group_by(Individual, Sites) %>%
  summarise(time_spent = max(Date) - min(Date))
#> # A tibble: 3 x 3
#> # Groups:   Individual [2]
#>   Individual Sites time_spent  
#>   <fct>      <dbl> <time>      
#> 1 A              4 2.00647 days
#> 2 B              6 0.00000 days
#> 3 B              7 0.00000 days

^{Created on 2019-03-20 by the reprex package (v0.2.1)}