Start and end dates

Marsel Scheer

2019-12-28

Introduction

The duration of a task is defined by the two columns start and end, which can be implicitly (due to dependencies and estimated durations of a task) or explicitly defined.

Explicit start and end dates

This is the easiest case. Just provide the date in the format yyyy-mm-dd for start and end date. If you use a Excel dates are stored as numeric numbers. In order convert this numeric back to a date a origin is necessary, which can be passed to projectPlan::wrangle_raw_plan. Unfortunately, Excel uses two different origins. For dates (post-1901) from Windows Excel origin should be 1899-12-30 (is the default value). For dates (post-1901) from Mac Excel origin should be 1904-01-01.

One possible workflow is to set the start date to the actual date when the task was started. This way it is directly documented when the task was started and also to set the actual end date once the task was completed.

pA <- dplyr::tibble(
  project = c("A"), 
  section = "prep", task = paste0("task", 1:2), id = paste0("i", 1:2), 
  start = c("2018-12-10", "2018-12-11"),
  end   = c("2018-12-15", "2018-12-12"),
  progress = 0, 
  resource = "R1")
DT::datatable(pA)

All dates are interpreted as ‘begin of business day’ (BOB) which is just a conventation made for this package. Of course, it would also be reasonable to define the end date as ‘end of busibness day’. However, there is already a third date and other dates might follow. Hence, it is probably easier to always think in BOB. So a task that started on 2018-12-10 and ended on 2018-12-11 was accomplished within one day.

Implicit start and end dates

Lets look at a simple dependency, where id i2 depends on id i1, which it self is implicitly defined by the TODAY-entry in column start:

pA <- dplyr::tibble(
  project = c("A"), 
  section = "prep", task = paste0("task", 1:2), id = paste0("i", 1:2), 
  start = c("TODAY", NA_character_),
  end   = c(NA_character_, NA_character_),
  depends_on = c(NA_character_, "i1"),
  est_duration = c(2,4),
  deadline = c(NA_character_, NA_character_),
  status = c("", ""),
  progress = 0, 
  resource = "R1")
DT::datatable(pA)

Wrangling this simple plan allows to calculate the timelines for both tasks:

pA %>% 
  projectPlan::wrangle_raw_plan() %>% 
  calculate_time_lines() %>% 
  select(task, time_start, time_end) %>% 
  DT::datatable()
#> WARN -- 2019-12-28 09:25:59 -- projectPlan/h.exclude_weekends(earliest_start_time, end): start 2019-12-28 is on a weekend. Shift end 2019-12-30 by 2 day(s).

Note that TODAY for the start time of id i1 was subsituted by the date the function projectPlan::wrangle_raw_plan was executed.

See the corresponding vignette for more details on id’s and dependencies.