Question

How could I use the sort-regexp-fields to emulate the sort-numeric-fields. I tried like this:

123
345
90
80
1999

M-x sort-regexp-fields

Regexp specifying records to sort: \ ([0-9]+\)

Regexp specifying key within record: \, \#1

But it can’t work.
what I really want to sort is something like this:

foo index: 123
index: 345 boo
…

the question is: I want to sort the lines by the number after the word “index”, but the number is not in the same field, they just have a word “index” before it. what should I do to complete this? anybody can help me?

Answer 1

sort-regexp-fields doesn’t do lexicographical compare, and there’s no trivial way to get it to do that. That said, we can use a trick of defining our own command, and using that command to signal to some advice to shoe-horn in a lexicographical compare.

The following command does what you want, provided you mark the region around the lines you want to compare:

(defun my-line-sort (begin end)
  (interactive "r")
  (sort-regexp-fields nil "^.*: +\\([0-9]+\\).*$" "\\1" begin end))

(defun compare-buffer-substrings-lexigraphically (b1 b2)
  (< (string-to-number (buffer-substring-no-properties (car b1) (cdr b1)))
     (string-to-number (buffer-substring-no-properties (car b2) (cdr b2)))))

(defadvice sort-subr (before sort-subr-lexical-compare activate)
  "In special case, force predicate to be a lexical compare"
  (when (eq this-command 'my-line-sort)
    (ad-set-arg 5 'compare-buffer-substrings-lexigraphically)))