A core part of my note-taking strategy is a growing collection of Emacs Org mode files containing my monthly lab journals, project summaries and various technical documents.

Usually I rely on Projectile’s Helm integration to perform recursive searches with The Silver Searcher (ag) using helm-projectile-ag (trigged by the completely muscle-memorised C-c p s s) through all of the org files in my notes hierarchy. Recursive regular expression search results are shown interactively as you type. Wonderful!

However, recently I found that I really missed the ability to see my search results sorted by last modified date, so that the most recently touched files would show up first. For a chronological notes database, this sorting makes the most sense.

A few frustrating hours later, interspersed with bouts of seriously pondering the exact nature of my relationship with Emacs, I managed to attain the desired result using the Emacs packages ivy and counsel.

Although I’m sticking with Helm for the rest, in this case the ivy API made it much simpler to do what I needed to do. It is understandable that this is not a straight-forward endeavour, as ag is heavily parallelised and furthermore is handled asynchronously by both helm and ivy / counsel. Sorting the results slows matters down, but for this specific case the slowdown is a reasonable price to pay.

Video demo of end result

If you follow the instruction below, you too will be able to achieve the following feats of recall:

Search results are returned as I type, as is usually the case with counsel-ag and helm-ag. However, they are now sorted by file modified date, last modified file at the top. This usually means I find what I need faster.

Show me the code

The ivy-read function (this is ivy’s single API entrypoint) has two required parameters, one of which is the collection. This is a function returning the list of items that the user wants to narrow down, or the list itself.

Because we need to tell ivy to sort the results by associating a sorting function with a specific collection function, we wrap the supplied counsel-ag-function collection function.

We also supply a new sorting function that will take two of the ag-generated search results, each of the form relative_filename:line_number:line_contents, derive the filenames from that, determine the modified timestamps of both the files and then return t or nil depending on which file is newer.

We finally (for this first snippet) associate the sorting function with our wrapped collection function.

(defun cpb/ag-collection (string)
"Search for pattern STRING using ag.
We only have this as a separate function so we can assoc with sort function."
;; this will use counsel--async-command to run asynchronously
(counsel-ag-function string counsel-ag-base-command ""))

;; modified from https://github.com/abo-abo/swiper/wiki/Sort-files-by-mtime
;; * directory to counsel--git-grep-dir: that's where AG is working
;; * removed directory logic: ag returns files
;; * parsed out filename from ag results
(defun eh-ivy-sort-file-by-mtime (x y)
"Determine if AG sort result X is newer than Y."
(let* ((x (concat counsel--git-grep-dir (car (split-string x ":"))))
(y (concat counsel--git-grep-dir (car (split-string y ":"))))
(x-mtime (nth 5 (file-attributes x)))
(y-mtime (nth 5 (file-attributes y))))
(time-less-p y-mtime x-mtime)))

;; ivy uses the ivy-sort-functions-alist to look up suitable sort
;; functions for any given collection function
;; we add a cons cell specifying eh-ivy-sort-file-by-mtime as the sort
;; function to go with our collection function
'(cpb/ag-collection . eh-ivy-sort-file-by-mtime))


In the second and final snippet, we create a new version of the counsel-ag function where we specify our own collection function, and we supply a truthful :sort argument.

(defun cpb/counsel-ag (&optional initial-input initial-directory extra-ag-args ag-prompt)
"Grep for a string in the current directory using ag.
INITIAL-INPUT can be given as the initial minibuffer input.
INITIAL-DIRECTORY, if non-nil, is used as the root directory for search.
EXTRA-AG-ARGS string, if non-nil, is appended to counsel-ag-base-command'.
AG-PROMPT, if non-nil, is passed as ivy-read' prompt argument.

(interactive)
(when current-prefix-arg
(setq initial-directory
(or initial-directory
(car (split-string counsel-ag-base-command))
" in directory: "))))
(setq extra-ag-args
(or extra-ag-args
(let* ((pos (cl-position ?  counsel-ag-base-command))
(command (substring-no-properties counsel-ag-base-command 0 pos))
(ag-args (replace-regexp-in-string
"%s" "" (substring-no-properties counsel-ag-base-command pos))))
(read-string (format "(%s) args:" command) ag-args)))))
(ivy-set-prompt 'cpb/counsel-ag counsel-prompt-function)
(setq counsel--git-grep-dir (or initial-directory default-directory))
(ivy-read (or ag-prompt (car (split-string counsel-ag-base-command)))
#'cpb/ag-collection
:initial-input initial-input
:dynamic-collection t
;; yes, we want to sort the results
:sort t
:keymap counsel-ag-map
:history 'counsel-git-grep-history
:action #'counsel-git-grep-action
:unwind (lambda ()
(counsel-delete-process)
(swiper--cleanup))
:caller 'cpb/counsel-ag))


Closing

You can invoke cpb/counsel-ag interactively to search from the current directory, or you can point it at a directory of your choosing by passing in the initial-directory argument.

In my Emacs initialisation, I have bound another wrapper function, bound to a global shortcut key, that invokes cpb/counsel-ag on my notes directory, so I can instantly search through my notes in reverse chronological order.

It looks like this:

;; wrapper function to invoke chrono-sorted ag search on my notes dir
(defun cpb/counsel-ag-notes ()
"Search my notes file hierarchy using counsel and ivy."
(interactive)
(cpb/counsel-ag nil "~/Dropbox/notes/pkb4000/" nil "PKB4000: "))

;; I invoke search by pressing "Ctrl-C 4"
(global-set-key (kbd "C-c 4") 'cpb/counsel-ag-notes)


I believe that my relationship with Emacs is safe for now.

• 2017-02-28: Fixed (interactive) invocation in wrapper function.
• 2017-02-27: Updated cpb/ag-collection for latest counsel version. Added example of wrapper function and global shortcut.