reprex.R

``` r
library(tidyverse)
library(lubridate)
#> 
#> Attachement du package : 'lubridate'
#> The following object is masked from 'package:base':
#> 
#>     date
df <- tibble(Evt = c("F", "O", "F", "O", "O", "F", "F"), 
             date_time = as_datetime(c("2019-01-22 09:37:56", 
                           "2019-01-22 09:37:57",
                           "2019-01-22 09:37:58",
                           "2019-01-22 09:37:59",
                           "2019-01-22 09:38:56",
                           "2019-01-22 09:38:58",
                           "2019-01-22 09:38:59")))

df
#> # A tibble: 7 x 2
#>   Evt   date_time          
#>   <chr> <dttm>             
#> 1 F     2019-01-22 09:37:56
#> 2 O     2019-01-22 09:37:57
#> 3 F     2019-01-22 09:37:58
#> 4 O     2019-01-22 09:37:59
#> 5 O     2019-01-22 09:38:56
#> 6 F     2019-01-22 09:38:58
#> 7 F     2019-01-22 09:38:59
```

<sup>Created on 2019-01-30 by the [reprex package](https://reprex.tidyverse.org) (v0.2.1)</sup>