Retrieve the total time CLOCKED over a given interval

Question

Question: How can I retrieve, over a set of files S (in particular: over my agenda files + their archive files) the total time clocked (as the return value of an elisp function; not as a clock table)? So for example, if I have:

* Header1
  :LOGBOOK:
  CLOCK: [2019-05-01 Sat 18:10]--[2019-05-01 Sat 18:30] =>  0:20
  :END:

# File2
* Header2
  :LOGBOOK:
  CLOCK: [2019-05-11 Sat 18:10]--[2019-05-11 Sat 18:11] =>  0:01
  :END:
* Header3
  :LOGBOOK:
  CLOCK: [2019-05-11 Sat 18:10]--[2019-05-11 Sat 18:20] =>  0:10
  :END:

I'd like to run a function like (sum-all-time-from "[2019-05-10]" "[2019-05-12]") to get as answer ~0:11~.

Answer 1

Here's how you can sum the times of each subtree within a time range (deprecated):

(org-map-entries
 (lambda ()
   (org-duration-from-minutes
    (org-clock-sum "[2019-05-10]" "[2019-05-12]")))
 nil 'agenda-with-archives)

---

The org-clock-sum function is run on every subtree in the buffer, but since we are using org-map-entries we probably only need to run org-clock-sum once with the subtree narrowed. If anything this function should run a lot faster:

(org-duration-from-minutes
 (apply '+ (org-map-entries
            (lambda ()
              (save-restriction
                (org-narrow-to-subtree)
                (org-clock-sum "[2019-05-10]" "[2019-05-12]")))
            nil 'agenda-with-archives)))

Here's an explanation of what each part of the function does: First, org-map-entries calls org-clock-sum at each headline of the agenda files and any archive files associated with them, but to avoid repetition, org-clock-sum is run with the subtree narrowed. Lastly, we add the time sum of all subtrees and use org-duration-from-minutes to get the duration string of the number of minutes, so that 61 minutes becomes "1:01" and so on.