Given question: provided a dataset with employee id, clock in, and clock out data... how would you get hourly counts of employees on the clock?

count-workers.R

# Libraries
library(tidyverse, quietly = TRUE)
library(lubridate, warn.conflicts = FALSE, quietly = TRUE)

# Create simulated data set
set.seed(123)
possible_starts <- seq.POSIXt(ymd_hms("2018-10-30 09:00:00"), ymd_hms("2018-10-30 14:00:00"), by = "min")
possible_ends <- seq.POSIXt(ymd_hms("2018-10-30 14:00:00"), ymd_hms("2018-10-30 20:00:00"), by = "min")

(work_times <- tibble(worker_id = 1:100,
                      start = sample(possible_starts, 100, TRUE),
                      end = sample(possible_ends, 100, TRUE)))
#> # A tibble: 100 x 3
#>    worker_id start               end                
#>        <int> <dttm>              <dttm>             
#>  1         1 2018-10-30 10:26:00 2018-10-30 17:36:00
#>  2         2 2018-10-30 12:57:00 2018-10-30 16:00:00
#>  3         3 2018-10-30 11:03:00 2018-10-30 16:56:00
#>  4         4 2018-10-30 13:25:00 2018-10-30 19:44:00
#>  5         5 2018-10-30 13:43:00 2018-10-30 16:54:00
#>  6         6 2018-10-30 09:13:00 2018-10-30 19:21:00
#>  7         7 2018-10-30 11:38:00 2018-10-30 19:30:00
#>  8         8 2018-10-30 13:28:00 2018-10-30 17:39:00
#>  9         9 2018-10-30 11:45:00 2018-10-30 16:28:00
#> 10        10 2018-10-30 11:17:00 2018-10-30 14:53:00
#> # ... with 90 more rows

# Create expanded vectors for hours-->unnest-->group-->count 
(hourly_counts <- work_times %>% 
  mutate_if(is.POSIXt, funs(floor_date(., unit = "hours"))) %>% 
  mutate(hours_worked = map2(start, end, seq.POSIXt, by = "hour")) %>% 
  unnest(hours_worked) %>% 
  count(hours_worked))
#> # A tibble: 11 x 2
#>    hours_worked            n
#>    <dttm>              <int>
#>  1 2018-10-30 09:00:00    19
#>  2 2018-10-30 10:00:00    39
#>  3 2018-10-30 11:00:00    60
#>  4 2018-10-30 12:00:00    81
#>  5 2018-10-30 13:00:00   100
#>  6 2018-10-30 14:00:00   100
#>  7 2018-10-30 15:00:00    90
#>  8 2018-10-30 16:00:00    70
#>  9 2018-10-30 17:00:00    50
#> 10 2018-10-30 18:00:00    29
#> 11 2018-10-30 19:00:00    18