Emacs org-mode dynamic block similar to clocktable, but grouped by tag See: http://stackoverflow.com/q/17353591/1225607

clocktable-by-tag.el

(defun clocktable-by-tag/shift-cell (n)
  (let ((str ""))
    (dotimes (i n)
      (setq str (concat str "| ")))
    str))

(defun clocktable-by-tag/insert-tag (params)
  (let ((tag (plist-get params :tags)))
    (insert "|--\n")
    (insert (format "| %s | *Tag time* |\n" tag))
    (let ((total 0))
      (mapcar
       (lambda (file)
         (let ((clock-data (with-current-buffer (find-file-noselect file)
                             (org-clock-get-table-data (buffer-name) params))))
           (when (> (nth 1 clock-data) 0)
             (setq total (+ total (nth 1 clock-data)))
             (insert (format "| | File *%s* | %.2f |\n"
                             (file-name-nondirectory file)
                             (/ (nth 1 clock-data) 60.0)))
             (dolist (entry (nth 2 clock-data))
               (insert (format "| | . %s%s | %s %.2f |\n"
                               (org-clocktable-indent-string (nth 0 entry))
                               (nth 1 entry)
                               (clocktable-by-tag/shift-cell (nth 0 entry))
                               (/ (nth 3 entry) 60.0)))))))
       (org-agenda-files))
      (save-excursion
        (re-search-backward "*Tag time*")
        (org-table-next-field)
        (org-table-blank-field)
        (insert (format "*%.2f*" (/ total 60.0)))))
    (org-table-align)))

(defun org-dblock-write:clocktable-by-tag (params)
  (insert "| Tag | Headline | Time (h) |\n")
  (insert "|     |          | <r>  |\n")
  (let ((tags (plist-get params :tags)))
    (mapcar (lambda (tag)
              (setq params (plist-put params :tags tag))
              (clocktable-by-tag/insert-tag params))
            tags)))

@ffevotte I've extended this solution and packaged it as clocktable-by-tag. Are you okay if I add it into MELPA (which requires setting a GPL-compatible license)?