Implemented filtering of an existing agenda view with respect to a tag.

ORGWEBPAGE/Changes.org

@@ -32,6 +32,27 @@
 
 ** Details
 
+*** Secondary filtering of agenda views.
+
+    You can now easily and interactively filter an existing
+    agenda view with respect to a tag.  This command is executed
+    with the =/= key in the agenda.  You will be prompted for a
+    tag selection key, and all entries that do not contain or
+    inherit the corresponding tag will be removed from the agenda
+    view.  With a prefix argument, the complementary filter is
+    applied: entries that do have the tag will be removed.
+    Narrowing the search results down with several successive
+    filtering operations is possible.
+
+    Note that this only removes the entries from the agenda
+    buffer, but it does not modify the query.  Therefore, the =r=
+    and =g= keys will restore the original agenda buffer.
+
+    This functionality was John Wiegleys idea and is a simpler
+    implementation of some of the query-editing features proposed
+    and implemented some time ago by Christopher League (see the
+    file contrib/lisp/org-interactive-query.el).
+
 *** Editing fixed-width regions with picture or artist mode
 
     The command @<code>C-c '@</code> (that is =C-c= followed by a

doc/org.texi

@@ -5800,21 +5800,28 @@ that entry would be in the original buffer (taken from a property, from a
 @code{#+COLUMNS} line, or from the default variable
 @code{org-columns-default-format}), will be used in the agenda.
 
-@tsubheading{Query editing}
+@tsubheading{Secondary filtering and query editing}
 @cindex query editing, in agenda
 
+@kindex /
+@item /
+Filter the current agenda view with respect to a tag.  You will be prompted
+for a tag selection letter and all entries that do not contain this tag will
+be removed from the agenda display.  When called with prefix arg, remove the
+entries that @emph{do} have the tag.
+
 @kindex [
 @kindex ]
 @kindex @{
 @kindex @}
 @item [ ] @{ @}
-In the @i{search view} (@pxref{Keyword search}), these keys add new
-search words (@kbd{[} and @kbd{]}) or new regular expressions (@kbd{@{}
-and @kbd{@}}) to the query string.  The opening bracket/brace will add a
-positive search term prefixed by @samp{+}, indicating that this search
-term @i{must} occur/match in the entry.  Closing bracket/brace add a
-negative search term which @i{must not} occur/match in the entry for it
-to be selected.
+In the @i{search view} (@pxref{Keyword search}), these keys add new search
+words (@kbd{[} and @kbd{]}) or new regular expressions (@kbd{@{} and
+@kbd{@}}) to the query string.  The opening bracket/brace will add a positive
+search term prefixed by @samp{+}, indicating that this search term @i{must}
+occur/match in the entry.  The closing bracket/brace will add a negative
+search term which @i{must not} occur/match in the entry for it to be
+selected.
 
 
 @tsubheading{Remote editing}

lisp/ChangeLog

@@ -1,5 +1,7 @@
 2008-09-05  Carsten Dominik  <dominik@science.uva.nl>
 
+	* org-agenda.el (org-agenda-filter-by-tag): New command.
+
 	* org-exp.el (org-get-current-options): Remove angular brackets
 	from the date entry.
 

lisp/org-agenda.el

@@ -1159,6 +1159,7 @@ The following commands are available:
 (org-defkey org-agenda-mode-map "]" 'org-agenda-manipulate-query-subtract)
 (org-defkey org-agenda-mode-map "{" 'org-agenda-manipulate-query-add-re)
 (org-defkey org-agenda-mode-map "}" 'org-agenda-manipulate-query-subtract-re)
+(org-defkey org-agenda-mode-map "/" 'org-agenda-filter-by-tag)
 
 (defvar org-agenda-keymap (copy-keymap org-agenda-mode-map)
   "Local keymap for agenda entries from Org-mode.")
@@ -4078,6 +4079,32 @@ When this is the global TODO list, a prefix argument will be interpreted."
     (goto-line line)
     (recenter window-line)))
 
+(defun org-agenda-filter-by-tag (strip &optional char)
+  "Keep only those lines in the agenda buffer that have a specific tag.
+The tag is selected with its fast selection letter, as configured.
+With prefix argument STRIP, remove all lines that do have the tag."
+  (interactive "P")
+  (let (char a tag (inhibit-read-only t))
+    (message "Tag selection character [%s]"
+	     (mapconcat
+	      (lambda (x) (if (cdr x) (char-to-string (cdr x)) ""))
+	      org-tag-alist-for-agenda ""))
+    (setq char (read-char-exclusive))
+    (unless (setq a (rassoc char org-tag-alist-for-agenda))
+      (error "invalid tag selection character %c" char))
+    (setq tag (car a))
+    (save-excursion
+      (goto-char (point-min))
+      (while (not (eobp))
+	(if (get-text-property (point) 'org-marker)
+	    (progn
+	      (setq tags (get-text-property (point) 'tags))
+	      (if (or (and (member tag tags) strip)
+		      (and (not (member tag tags)) (not strip)))
+		  (delete-region (point) (1+ (point-at-eol)))
+		(beginning-of-line 2)))
+	  (beginning-of-line 2))))))
+
 (defun org-agenda-manipulate-query-add ()
   "Manipulate the query by adding a search term with positive selection.
 Positive selection means, the term must be matched for selection of an entry."
@@ -5316,4 +5343,3 @@ belonging to the \"Work\" category."
 
 ;;; org-agenda.el ends here
 
-

lisp/org.el

@@ -1357,6 +1357,8 @@ taken from the (otherwise obsolete) variable `org-todo-interpretation'."
 (make-variable-buffer-local 'org-todo-keywords-1)
 (defvar org-todo-keywords-for-agenda nil)
 (defvar org-done-keywords-for-agenda nil)
+(defvar org-todo-keyword-alist-for-agenda nil)
+(defvar org-tag-alist-for-agenda nil)
 (defvar org-agenda-contributing-files nil)
 (defvar org-not-done-keywords nil)
 (make-variable-buffer-local 'org-not-done-keywords)
@@ -12216,6 +12218,11 @@ When a buffer is unmodified, it is just killed.  When modified, it is saved
 		(append org-todo-keywords-for-agenda org-todo-keywords-1))
 	  (setq org-done-keywords-for-agenda
 		(append org-done-keywords-for-agenda org-done-keywords))
+	  (setq org-todo-keyword-alist-for-agenda
+		(append org-todo-keyword-alist-for-agenda org-todo-key-alist))
+	  (setq org-tag-alist-for-agenda 
+		(append org-tag-alist-for-agenda org-tag-alist))
+
 	  (save-excursion
 	    (remove-text-properties (point-min) (point-max) pall)
 	    (when org-agenda-skip-archived-trees
@@ -12228,7 +12235,11 @@ When a buffer is unmodified, it is just killed.  When modified, it is saved
 	    (while (re-search-forward re nil t)
 	      (add-text-properties
 	       (match-beginning 0) (org-end-of-subtree t) pc)))
-	  (set-buffer-modified-p bmp))))))
+	  (set-buffer-modified-p bmp))))
+    (setq debug-on-error t)
+    (setq org-todo-keyword-alist-for-agenda
+	  (org-uniquify org-todo-keyword-alist-for-agenda)
+	  org-tag-alist-for-agenda (org-uniquify org-tag-alist-for-agenda))))
 
 ;;;; Embedded LaTeX