#+title:  Editing Data Files
#+author: Howard X. Abrams
#+date:   2022-10-14
#+tags: emacs

A literate programming file for configuring Emacs to edit files of data.

#+begin_src emacs-lisp :exports none
  ;;; ha-data --- edit data files. -*- lexical-binding: t; -*-
  ;;
  ;; © 2022-2023 Howard X. Abrams
  ;;   Licensed under a Creative Commons Attribution 4.0 International License.
  ;;   See http://creativecommons.org/licenses/by/4.0/
  ;;
  ;; Author: Howard X. Abrams <http://gitlab.com/howardabrams>
  ;; Maintainer: Howard X. Abrams
  ;; Created: October 14, 2022
  ;;
  ;; While obvious, GNU Emacs does not include this file or project.
  ;;
  ;; *NB:* Do not edit this file. Instead, edit the original literate file at:
  ;;            /Users/howard.abrams/other/hamacs/ha-data.org
  ;;       And tangle the file to recreate this one.
  ;;
  ;;; Code:
  #+end_src
* Introduction
Once upon a time, I [[https://www.youtube.com/watch?v=HKJMDJ4i-XI][gave a talk]] to EmacsConf 2019, about [[http://howardism.org/Technical/Emacs/piper-presentation-transcript.html][an interesting idea]] I called [[https://gitlab.com/howardabrams/emacs-piper][emacs-piper]]. I still like the idea of sometimes editing an Emacs buffer on the entire contents, as if it were a data file. This file contains what I feel are the best functions for that… oh, and a leader to call it (instead of the original Hydra).

#+begin_src emacs-lisp
  (ha-leader
    "d"   '(:ignore t :which-key "data")
    "d |" '("pipe to shell"  . replace-buffer-with-shell-command)
    "d r" '("replace buffer"  . ha-vr-replace-all)
    "d y" '("copy to clipboard" . ha-yank-buffer-contents))
#+end_src
** Global Replacements
The string replacement functions operate at the current point, which means I need to jump to the beginning before calling something like [[help:vr/replace][vr/replace]].

#+begin_src emacs-lisp
  (defun ha-vr-replace-all (regexp replace start end)
    "Regexp-replace entire buffer with live visual feedback."
    (interactive
     (vr--interactive-get-args 'vr--mode-regexp-replace 'vr--calling-func-replace))
    (vr/replace regexp replace (point-min) (point-max)))
#+end_src
* Line-Oriented Functions
These functions focus on the data in the buffer as a series of lines:
#+begin_src emacs-lisp
  (ha-leader
    "d l"   '(:ignore t :which-key "on lines")
    "d l d" '("flush lines"    . flush-lines)
    "d l k" '("keep lines"     . keep-lines)
    "d l s" '("sort lines"     . ha-sort-lines)
    "d l f" '("sort fields"    . ha-sort-fields)
    "d l n" '("sort field num" . ha-sort-fields-numerically)
    "d l r" '("reverse lines"  . ha-reverse-lines)
    "d l u" '("unique lines"   . delete-duplicate-lines)
    "d l b" '("flush blanks"   . flush-blank-lines))
#+end_src

One issue I have is [[help:keep-lines][keep-lines]] operate on the lines /starting with the point/, not on the entire buffer. Let’s fix that:
#+begin_src emacs-lisp
  (defun call-function-at-buffer-beginning (orig-fun &rest args)
    "Call ORIG-FUN after moving point to beginning of buffer.
  Point restored after completion. Good for advice."
    (save-excursion
      (goto-char (point-min))
      (apply orig-fun args)))

  (advice-add 'keep-lines :around #'call-function-at-buffer-beginning)
  (advice-add 'flush-lines :around #'call-function-at-buffer-beginning)
#+end_src

The [[help:sort-lines][sort-lines]] is useful, but insists on an /active/ region. Let’s make a collection of data-focused versions that work on both a region (if it is active) or the entire buffer, regardless of the position of the cursor.
#+begin_src emacs-lisp
  (dolist (tuple '((ha-sort-lines sort-lines)
                   (ha-sort-fields sort-fields)
                   (ha-sort-fields-numerically sort-numeric-fields)))
    (cl-destructuring-bind (func orig-func) tuple
      (eval `(defun ,func (prefix)
               ,(format "Call `%s' with all lines in a buffer or region (if active).
  Passes PREFIX to the function." orig-func)
               (interactive "P")
               (save-excursion
                 (if (region-active-p)
                     (,orig-func prefix (region-beginning) (region-end))
                   (,orig-func prefix (point-min) (point-max))))))))
#+end_src

Getting rid of blank lines seems somewhat useful:
#+begin_src emacs-lisp
  (defun flush-blank-lines ()
    "Delete all empty lines in the buffer. See `flush-lines'."
    (interactive)
    (save-excursion
      (goto-char (point-min))
      (flush-lines (rx line-start (zero-or-more space) line-end))))
#+end_src
* Table-Oriented Functions
These functions focus on the data in the buffer as a table consisting of columns and rows of some sort.
#+begin_src emacs-lisp
  (ha-leader
    "d t"   '(:ignore t :which-key "on tables")
    "d t f" '("sort by columns"    . ha-sort-fields)
    "d t n" '("sort by columns numerically" . ha-sort-fields-numerically)
    "d t k" '("keep columns" . keep-columns)
    "d t f" '("flush columns" . flush-columns))
#+end_src

Each of the /table/ functions require a /table separator/ (for instance the =|= character) and often the columns to operate on.
The =keep-columns= removes all text, except for /indexed/ text between the separator:
#+begin_src emacs-lisp
  (defun keep-columns (separator columns)
    "Keep tabular text columns, deleting the rest in buffer or region.
  Defined columns as text between SEPARATOR, not numerical
  position. Note that text _before_ the separator is column 0.

  For instance, given the following table:

     apple : avocado : apricot
     banana : blueberry : bramble
     cantaloupe : cherry : courgette : cucumber
     data : durian

  Calling this function with a `:' character, as columns: `0, 2'
  results in the buffer text:

     apple : apricot
     banana : bramble
     cantaloupe : courgette
     data : durian"
    (interactive "sSeparator: \nsColumns to Keep: ")
    (operate-columns separator columns t))
#+end_src

The =flush-columns= is similar, except that is deletes the given columns.
#+begin_src emacs-lisp
  (defun flush-columns (separator columns)
    "Delete tabular text columns in buffer or region.
  Defined columns as text between SEPARATOR, not numerical
  position. Note that text _before_ the separator is column 0.

  For instance, given the following table:

     apple : avocado : apricot
     banana : blueberry : bramble
     cantaloupe : cherry : courgette : cucumber
     data : durian

  Calling this function with a `:' character, as columns: `1'
  (remember the colums are 0-indexed),
  results in the buffer text:

     apple : avocado : apricot
     banana : blueberry : bramble
     cantaloupe : cherry : courgette : cucumber
     data : durian

     apple : apricot
     banana : bramble
     cantaloupe : courgette
     data : durian"
    (interactive "sSeparator: \nsColumns to Delete: ")
    (operate-columns separator columns nil))
#+end_src

Both functions are similar, and their behavior comes from =operate-columns=, which walks through the buffer, line-by-line:
#+begin_src emacs-lisp
  (defun operate-columns (separator columns-str keep?)
    "Call `operate-columns-on-line' for each line in buffer.
  First, convert string COLUMNS-STR to a list of number, then
  search for SEPARATOR."
    (let ((columns (numbers-to-number-list columns-str)))
      (save-excursion
        (when (region-active-p)
          (narrow-to-region (region-beginning) (region-end)))
        (goto-char (point-min))
        (while (re-search-forward (rx (literal separator)) nil t)
          (operate-columns-on-line separator columns t)
          (next-line)))))
#+end_src

For each line, the =operate-columns= calls this function:
#+begin_src emacs-lisp
  (defun operate-columns-on-line (separator columns keep?)
    "Replace current line after keeping or deleting COLUMNS.
  Keep the COLUMNS if KEEP? is non-nil, delete otherwise.
  Defined columns as the text between SEPARATOR."
    (cl-labels ((keep-oper (idx it) (if keep?
                                        (when (member idx columns) it)
                                      (unless (member idx columns) it))))
      (let* ((start (line-beginning-position))
             (end (line-end-position))
             (line (buffer-substring start end))
             (parts (thread-last (split-string line separator)
                                 (--map-indexed (keep-oper it-index it))
                                 (-remove 'null)))
             (nline (string-join parts separator)))
        (delete-region start end)
        (insert nline))))
#+end_src

I like the idea of the shell command, =cut=, where you can have an arbitrary character as a separator, and then either delete or keep the data between them, as columns. But I need a function that can convert a string of “columns”, for instance ="1, 4-7 9"= to an list of numbers, like ='(1 4 5 6 7 9)=:
#+begin_src emacs-lisp
  (defun numbers-to-number-list (input)
    "Convert the string, INPUT, to a list of numbers.
  For instance: `1, 4-7 9' returns `(1 4 5 6 7 9)'"
    (let* ((separator (rx (* space) (or "," space) (* space)))
           (dashed    (rx (* space) "-" (* space)))
           (ranged    (rx (group (+ digit)) (regexp dashed) (group (+ digit))))
           (str-list  (split-string input separator t)))
      (--reduce-from (append acc (if (string-match ranged it)
                                 (number-sequence
                                  (string-to-number (match-string 1 it))
                                  (string-to-number (match-string 2 it)))
                               (list (string-to-number it))))
                () str-list)))
#+end_src
Does this work?
#+begin_src emacs-lisp :tangle no
  (ert-deftest numbers-to-number-list-test ()
    (should (equal (numbers-to-number-list "2") '(2)))
    (should (equal (numbers-to-number-list "1, 2 3") '(1 2 3)))
    (should (equal (numbers-to-number-list "1, 4-7 9") '(1 4 5 6 7 9))))
#+end_src

The [[help:sort-fields][sort-fields]] function does a good job if the table is space separated, but if we separate by some other character(s), it doesn’t work. Can we write a function that does this? Here we make a /helper/ to some regular expression for the [[help:sort-regexp-fields][sort-regexp-fields]] function.
#+begin_src emacs-lisp
  (defun ha-sort-table-by-column (separator field)
    "Sort the active region or entire buffer by column, FIELD.
  Columns are denoted by a regular expression, SEPARATOR, which
  could be a single character. For instance, given a buffer:

   d, a, c, b
   x, y
   e, f, g
   i, m, a, o

  Calling this function with a `,' separator, and `2' for the
  column, would result in:

   d, a, c, b
   e, f, g
   i, m, a, o
   x, y"
    (interactive "sSeparator: \nnSorting field: ")
    ;; Create a regular expression of grouped fields, separated
    ;; by the separator sequence, for commas, this would be e.g.
    ;;    \\(.*\\),\\(.*\\),\\(.*\\),\\(.*\\)
    (let* ((rx-list (mapconcat (lambda (x) (rx (group (zero-or-more any))))
                               (number-sequence 1 field)
                               separator))
           ;; Prepend the beginning of line to the regular expression:
           (regexp (concat (rx bol) rx-list))
           (start  (if (region-active-p) (region-beginning) (point-min)))
           (end    (if (region-active-p) (region-end)       (point-max))))
      (save-excursion
        (sort-regexp-fields nil regexp (format "\\%d" field) start end))))
#+end_src
* Buffer-Oriented Functions
If there is no specific function, but you can think of a shell command that will work, then
#+begin_src emacs-lisp
(defun replace-buffer-with-shell-command (command)
  "Replaces the contents of the buffer, or the contents of the
selected region, with the output from running an external
executable, COMMAND.

This is a wrapper around `shell-command-on-region'."
  (interactive "sCommand: ")
  (save-excursion
    (save-restriction
      (when (region-active-p)
        (narrow-to-region (region-beginning) (region-end)))
      (shell-command-on-region (point-min) (point-max) command nil t))))
#+end_src

* Technical Artifacts                                :noexport:
Let's =provide= a name so we can =require= this file:
#+begin_src emacs-lisp :exports none
  (provide 'ha-data)
  ;;; ha-data.el ends here
  #+end_src

#+description: configuring Emacs to edit files of data.

#+property:    header-args:sh :tangle no
#+property:    header-args:emacs-lisp  :tangle yes
#+property:    header-args    :results none :eval no-export :comments no mkdirp yes

#+options:     num:nil toc:t todo:nil tasks:nil tags:nil date:nil
#+options:     skip:nil author:nil email:nil creator:nil timestamp:nil
#+infojs_opt:  view:nil toc:t ltoc:t mouse:underline buttons:0 path:http://orgmode.org/org-info.js
