Revert `org-agenda-filter-by-category' to non-prompting state

doc/org-manual.org

@@ -9085,10 +9085,10 @@ filter types.
 - {{{kbd(<)}}} (~org-agenda-filter-by-category~) ::
 
   #+findex: org-agenda-filter-by-category
-  Prompt for a category, defaulting to the category of the item at
-  point, and show only entries with this category.  Pressing
-  {{{kbd(<)}}} again removes this filter.  When called with a prefix
-  argument exclude the category of the item at point from the agenda.
+  Filter by category of the line at point, and show only entries with
+  this category.  Pressing {{{kbd(<)}}} again removes this filter.
+  When called with a prefix argument exclude the category of the item
+  at point from the agenda.
 
 - {{{kbd(=)}}} (~org-agenda-filter-by-regexp~) ::
 
@@ -9125,12 +9125,20 @@ filter types.
   condition.  With two universal prefix arguments, it clears effort
   filters, which can be accumulated.
 
+- {{{kbd(^)}}} (~org-agenda-filter-by-top-headline~) ::
+
+  #+findex: org-agenda-filter-by-top-headline
+  Filter the current agenda view and only display items that fall
+  under the same top-level headline as the current entry.  So this
+  simulated the effect of restricting the agenda creation to this
+  tree.
+
 - {{{kbd(/)}}} (~org-agenda-filter~) ::
 
   #+findex: org-agenda-filter
-  This is the unified interface to all four filter methods described
-  above.  At the prompt, specify different filter elements in a single
-  string, with full completion support.  For example,
+  This a the unified interface to four of the five filter methods
+  described above.  At the prompt, specify different filter elements
+  in a single string, with full completion support.  For example,
 
   #+begin_example
      +work-John+<0:10-/plot/
@@ -9148,14 +9156,6 @@ filter types.
   the front of the string, the new filter elements are added to the
   active ones.
 
-- {{{kbd(^)}}} (~org-agenda-filter-by-top-headline~) ::
-
-  #+findex: org-agenda-filter-by-top-headline
-  Filter the current agenda view and only display items that fall
-  under the same top-level headline as the current entry.  So this
-  simulated the effect of restricting the agenda creation to this
-  tree.
-
 - {{{kbd(|)}}} (~org-agenda-filter-remove-all~) ::
 
   Remove all filters in the current agenda view.

lisp/org-agenda.el

@@ -7464,7 +7464,26 @@ With a prefix argument, do so in all agenda buffers."
   "Return the category of the agenda line."
   (org-get-at-bol 'org-category))
 
-  
+(defun org-agenda-filter-by-category (strip)
+  "Filter lines in the agenda buffer that have a specific category.
+The category is that of the current line.
+Without prefix argument, keep only the lines of that category.
+With a prefix argument, exclude the lines of that category."
+  (interactive "P")
+  (if (and org-agenda-filtered-by-category
+	   org-agenda-category-filter)
+      (org-agenda-filter-show-all-cat)
+    (let ((cat (org-no-properties (org-get-at-eol 'org-category 1))))
+      (cond
+       ((and cat strip)
+        (org-agenda-filter-apply
+         (push (concat "-" cat) org-agenda-category-filter) 'category))
+       (cat
+        (org-agenda-filter-apply
+         (setq org-agenda-category-filter
+	       (list (concat "+" cat))) 'category))
+       (t (error "No category at point"))))))
+
 (defun org-agenda-filter-by-category (strip)
   "Filter lines in the agenda buffer that have a specific category.
 The category is that of the current line.