hamacs/ha-data.org

Editing Data Files

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

Introduction

Once upon a time, I gave a talk to EmacsConf 2019, about an interesting idea I called 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).

  (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))

Global Replacements

The string replacement functions operate at the current point, which means I need to jump to the beginning before calling something like vr/replace.

  (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)))

Line-Oriented Functions

These functions focus on the data in the buffer as a series of lines:

  (ha-leader
    "d l"   '(:ignore t :which-key "on lines")
    "d l f" '("flush lines"         . flush-lines)
    "d l k" '("keep lines"          . keep-lines)
    "d l s" '("sort lines"          . ha-sort-lines)
    "d l u" '("unique lines"        . delete-duplicate-lines)
    "d l b" '("flush blanks"        . flush-blank-lines))

One issue I have is keep-lines operate on the lines starting with the point, not on the entire buffer. Let’s fix that:

  (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)

The sort-lines is useful, but insists on an active region. Let’s made a data-focused version:

  (defun ha-sort-lines (prefix)
    "Sort the lines in a buffer or region (if active).
  If PREFIX given, sort in reverse order."
    (interactive "P")
    (save-excursion
      (if (region-active-p)
          (sort-lines prefix (region-beginning) (region-end))
        (sort-lines prefix (point-min) (point-max)))))

Getting rid of blank lines seems somewhat useful:

  (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))))

Table-Oriented Functions

These functions focus on the data in the buffer as a table consisting of columns and rows of some sort.

  (ha-leader
    "d t"   '(:ignore t :which-key "on tables")
    "d t k" '("keep columns" . keep-columns)
    "d t f" '("flush columns" . flush-columns))

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:

  (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))

The flush-columns is similar, except that is deletes the given columns.

  (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))

Both functions are similar, and their behavior comes from operate-columns, which walks through the buffer, line-by-line:

  (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)))))

For each line, the operate-columns calls this function:

  (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))))

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):

  (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)))

Does this work?

  (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))))

Buffer-Oriented Functions

If there is no specific function, but you can think of a shell command that will work, then

(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))))