Re: How to get time difference with Elisp?

[Karl Voit]

* Karl Voit <devnull@Karl-Voit.at> wrote:
>
> I need to determine total office hours of a day without the time
> spent in lunch break. The source data is officebegin, officeend,
> lunchbreakbegin, lunchbreakend - all in string format "HH:MM" like
> "14:58".
>
> So far, I failed miserably to find the right combination of
> parse-time-string, encode-time, time-substract.

I chose the path I understood and which tends to be the easiest one:
manually converting everything to seconds, do the calculations, and
re-convert the results to HH:MM format.

Yes, I did not spend effort in error-proning, edge-cases and other
cases than same-day scenarios.

(defun my-extract-minutes-of-hm-string(hm-string)
  "returns the minutes of a string like 9:42 -> 42 (and 0 if there are no 
minutes)"
  (let (
    ;; minutes is the second element after splitting with ":"
    (minutes (nth 1 (split-string hm-string ":")))
    )
    ;; if there is no second element, return "0" (instead of nil)
    (if (eq minutes 'nil)
    0
      (string-to-number minutes)
      )
    )
  )

(defun my-extract-hours-of-hm-string(hm-string)
  "returns the hours of a string like 9:42 -> 9"
  (string-to-number
   (car
    (split-string hm-string ":")
    )
   )
)

(defun my-hm-string-to-minutes(hm-string)
  "returns the minutes of a string like 2:42 -> 162"
  (let (
    ;; minutes is the second element after splitting with ":"
    (minutes (my-extract-minutes-of-hm-string hm-string))
    (hours (my-extract-hours-of-hm-string hm-string))
    )
    (+ minutes (* hours 60))
    )
  )

(defun my-calculate-office-hour-total(officestart officeend lunchstart lunchend)
  "calculates the total hours:minutes of a work-day depending on time of 
arrival/leave and lunch break in HH:MM"
  (let (
    (officestartminutes (my-hm-string-to-minutes officestart));; integer of 
minutes
    (officeendminutes (my-hm-string-to-minutes officeend));; integer of minutes
    (lunchstartminutes (my-hm-string-to-minutes lunchstart));; integer of 
minutes
    (lunchendminutes (my-hm-string-to-minutes lunchend));; integer of minutes
    )
    (let* (
          (officeminutes (- (- officeendminutes officestartminutes) (- 
lunchendminutes lunchstartminutes)))
          (officeminutesstring (format-time-string "%H:%M" (seconds-to-time (* 
60 officeminutes)) t))
          )
      ;;(message (concat "Minutes epoch: " (number-to-string officeminutes)))
      ;;(message (concat "Minutes string: " officeminutesstring))
      (symbol-value 'officeminutesstring)
      )
    )
  )
;; (my-calculate-office-hour-total "09:57" "17:22" "11:35" "12:08") -> Minutes 
epoch: 412 | Minutes string: 06:52


Thanks for all the other approaches and snippets - I copied them to
my personal knowledge-collection to learn from them!

-- 
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