Fold region of org file

Question

Is there a way to fold a region in org-mode? (Not the whole file, and not an individual item, but a region containing multiple items.)

Often I want to collapse only a portion of an org file, say folding:

* a
** a1
** a2
* b
** b1
** b2
** b3
* c
** c1
** c2
* d
** d1
** d2

into

* a
** a1
** a2
* b ...
* c ...
* d
** d1
** d2

I know in this particular example I could simply fold the whole file using org-cycle, then expand a and d individually, but imagine there are hundreds of items and I want to fold a dozen contiguous items contained in an active region while leaving the rest of the items in the file expanded.

Answer 1

This seems to do what you want :

(defun org-hide-subtrees-in-region (beg end)
  (interactive "r")
  (save-restriction
    (narrow-to-region beg end)
    (outline-hide-sublevels 1)))

EDIT: I first gave a wrong solution, which I keep here as it is also interesting IMO (but doesn't answer the question)

The function outline-hide-region-body seems to be exactly what you want, but for some reason it is not interactive. We could add an interactive spec to it, but let's just define org-hide-subtrees-in-region as :

(defun org-hide-subtrees-in-region (beg end)
  (interactive "r")
  (outline-hide-region-body beg end))