-Sorting Text
-============
-
- The sorting functions described in this section all rearrange text in
-a buffer. This is in contrast to the function `sort', which rearranges
-the order of the elements of a list (*note Rearrangement::). The
-values returned by these functions are not meaningful.
-
- - Function: sort-subr reverse nextrecfun endrecfun &optional
- startkeyfun endkeyfun
- This function is the general text-sorting routine that divides a
- buffer into records and sorts them. Most of the commands in this
- section use this function.
-
- To understand how `sort-subr' works, consider the whole accessible
- portion of the buffer as being divided into disjoint pieces called
- "sort records". The records may or may not be contiguous; they may
- not overlap. A portion of each sort record (perhaps all of it) is
- designated as the sort key. Sorting rearranges the records in
- order by their sort keys.
-
- Usually, the records are rearranged in order of ascending sort key.
- If the first argument to the `sort-subr' function, REVERSE, is
- non-`nil', the sort records are rearranged in order of descending
- sort key.
-
- The next four arguments to `sort-subr' are functions that are
- called to move point across a sort record. They are called many
- times from within `sort-subr'.
-
- 1. NEXTRECFUN is called with point at the end of a record. This
- function moves point to the start of the next record. The
- first record is assumed to start at the position of point
- when `sort-subr' is called. Therefore, you should usually
- move point to the beginning of the buffer before calling
- `sort-subr'.
-
- This function can indicate there are no more sort records by
- leaving point at the end of the buffer.
-
- 2. ENDRECFUN is called with point within a record. It moves
- point to the end of the record.
-
- 3. STARTKEYFUN is called to move point from the start of a
- record to the start of the sort key. This argument is
- optional; if it is omitted, the whole record is the sort key.
- If supplied, the function should either return a non-`nil'
- value to be used as the sort key, or return `nil' to indicate
- that the sort key is in the buffer starting at point. In the
- latter case, ENDKEYFUN is called to find the end of the sort
- key.
-
- 4. ENDKEYFUN is called to move point from the start of the sort
- key to the end of the sort key. This argument is optional.
- If STARTKEYFUN returns `nil' and this argument is omitted (or
- `nil'), then the sort key extends to the end of the record.
- There is no need for ENDKEYFUN if STARTKEYFUN returns a
- non-`nil' value.
-
- As an example of `sort-subr', here is the complete function
- definition for `sort-lines':
-
- ;; Note that the first two lines of doc string
- ;; are effectively one line when viewed by a user.
- (defun sort-lines (reverse beg end)
- "Sort lines in region alphabetically.
- Called from a program, there are three arguments:
- REVERSE (non-nil means reverse order),
- and BEG and END (the region to sort)."
- (interactive "P\nr")
- (save-restriction
- (narrow-to-region beg end)
- (goto-char (point-min))
- (sort-subr reverse
- 'forward-line
- 'end-of-line)))
-
- Here `forward-line' moves point to the start of the next record,
- and `end-of-line' moves point to the end of record. We do not pass
- the arguments STARTKEYFUN and ENDKEYFUN, because the entire record
- is used as the sort key.
-
- The `sort-paragraphs' function is very much the same, except that
- its `sort-subr' call looks like this:
-
- (sort-subr reverse
- (function
- (lambda ()
- (skip-chars-forward "\n \t\f")))
- 'forward-paragraph)
-
- - Command: sort-regexp-fields reverse record-regexp key-regexp start
- end
- This command sorts the region between START and END alphabetically
- as specified by RECORD-REGEXP and KEY-REGEXP. If REVERSE is a
- negative integer, then sorting is in reverse order.
-
- Alphabetical sorting means that two sort keys are compared by
- comparing the first characters of each, the second characters of
- each, and so on. If a mismatch is found, it means that the sort
- keys are unequal; the sort key whose character is less at the
- point of first mismatch is the lesser sort key. The individual
- characters are compared according to their numerical values.
- Since Emacs uses the ASCII character set, the ordering in that set
- determines alphabetical order.
-
- The value of the RECORD-REGEXP argument specifies how to divide
- the buffer into sort records. At the end of each record, a search
- is done for this regular expression, and the text that matches it
- is the next record. For example, the regular expression `^.+$',
- which matches lines with at least one character besides a newline,
- would make each such line into a sort record. *Note Regular
- Expressions::, for a description of the syntax and meaning of
- regular expressions.
-
- The value of the KEY-REGEXP argument specifies what part of each
- record is the sort key. The KEY-REGEXP could match the whole
- record, or only a part. In the latter case, the rest of the
- record has no effect on the sorted order of records, but it is
- carried along when the record moves to its new position.
-
- The KEY-REGEXP argument can refer to the text matched by a
- subexpression of RECORD-REGEXP, or it can be a regular expression
- on its own.
-
- If KEY-REGEXP is:
-
- `\DIGIT'
- then the text matched by the DIGITth `\(...\)' parenthesis
- grouping in RECORD-REGEXP is the sort key.
-
- `\&'
- then the whole record is the sort key.
-
- a regular expression
- then `sort-regexp-fields' searches for a match for the regular
- expression within the record. If such a match is found, it
- is the sort key. If there is no match for KEY-REGEXP within
- a record then that record is ignored, which means its
- position in the buffer is not changed. (The other records
- may move around it.)
-
- For example, if you plan to sort all the lines in the region by the
- first word on each line starting with the letter `f', you should
- set RECORD-REGEXP to `^.*$' and set KEY-REGEXP to `\<f\w*\>'. The
- resulting expression looks like this:
-
- (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
- (region-beginning)
- (region-end))
-
- If you call `sort-regexp-fields' interactively, it prompts for
- RECORD-REGEXP and KEY-REGEXP in the minibuffer.
-
- - Command: sort-lines reverse start end
- This command alphabetically sorts lines in the region between
- START and END. If REVERSE is non-`nil', the sort is in reverse
- order.
-
- - Command: sort-paragraphs reverse start end
- This command alphabetically sorts paragraphs in the region between
- START and END. If REVERSE is non-`nil', the sort is in reverse
- order.
-
- - Command: sort-pages reverse start end
- This command alphabetically sorts pages in the region between
- START and END. If REVERSE is non-`nil', the sort is in reverse
- order.
-
- - Command: sort-fields field start end
- This command sorts lines in the region between START and END,
- comparing them alphabetically by the FIELDth field of each line.
- Fields are separated by whitespace and numbered starting from 1.
- If FIELD is negative, sorting is by the -FIELDth field from the
- end of the line. This command is useful for sorting tables.
-
- - Command: sort-numeric-fields field start end
- This command sorts lines in the region between START and END,
- comparing them numerically by the FIELDth field of each line. The
- specified field must contain a number in each line of the region.
- Fields are separated by whitespace and numbered starting from 1.
- If FIELD is negative, sorting is by the -FIELDth field from the
- end of the line. This command is useful for sorting tables.
-
- - Command: sort-columns reverse &optional beg end
- This command sorts the lines in the region between BEG and END,
- comparing them alphabetically by a certain range of columns. The
- column positions of BEG and END bound the range of columns to sort
- on.
-
- If REVERSE is non-`nil', the sort is in reverse order.
-
- One unusual thing about this command is that the entire line
- containing position BEG, and the entire line containing position
- END, are included in the region sorted.
-
- Note that `sort-columns' uses the `sort' utility program, and so
- cannot work properly on text containing tab characters. Use `M-x
- `untabify'' to convert tabs to spaces before sorting.
-
-\1f
-File: lispref.info, Node: Columns, Next: Indentation, Prev: Sorting, Up: Text
-
-Counting Columns
-================
-
- The column functions convert between a character position (counting
-characters from the beginning of the buffer) and a column position
-(counting screen characters from the beginning of a line).
-
- A character counts according to the number of columns it occupies on
-the screen. This means control characters count as occupying 2 or 4
-columns, depending upon the value of `ctl-arrow', and tabs count as
-occupying a number of columns that depends on the value of `tab-width'
-and on the column where the tab begins. *Note Usual Display::.