(emacs)Sorting


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Sorting Text
============

   Emacs provides several commands for sorting text in the buffer.  All
operate on the contents of the region (the text between point and the
mark).  They divide the text of the region into many "sort records",
identify a "sort key" for each record, and then reorder the records
into the order determined by the sort keys.  The records are ordered so
that their keys are in alphabetical order, or, for numeric sorting, in
numeric order.  In alphabetic sorting, all upper case letters `A'
through `Z' come before lower case `a', in accord with the ASCII
character sequence.

   The various sort commands differ in how they divide the text into
sort records and in which part of each record is used as the sort key.
Most of the commands make each line a separate sort record, but some
commands use paragraphs or pages as sort records.  Most of the sort
commands use each entire sort record as its own sort key, but some use
only a portion of the record as the sort key.

`M-x sort-lines'
     Divide the region into lines, and sort by comparing the entire
     text of a line.  A prefix argument means sort into descending
     order.

`M-x sort-paragraphs'
     Divide the region into paragraphs, and sort by comparing the entire
     text of a paragraph (except for leading blank lines).  A prefix
     argument means sort into descending order.

`M-x sort-pages'
     Divide the region into pages, and sort by comparing the entire
     text of a page (except for leading blank lines).  A prefix
     argument means sort into descending order.

`M-x sort-fields'
     Divide the region into lines, and sort by comparing the contents of
     one field in each line.  Fields are defined as separated by
     whitespace, so the first run of consecutive non-whitespace
     characters in a line constitutes field 1, the second such run
     constitutes field 2, etc.

     Specify which field to sort by with a numeric argument: 1 to sort
     by field 1, etc.  A negative argument means sort into descending
     order.  Thus, minus 2 means sort by field 2 in
     reverse-alphabetical order.  If several lines have identical
     contents in the field being sorted, they keep same relative order
     that they had in the original buffer.

`M-x sort-numeric-fields'
     Like `M-x sort-fields' except the specified field is converted to
     a number for each line, and the numbers are compared.  `10' comes
     before `2' when considered as text, but after it when considered
     as a number.

`M-x sort-columns'
     Like `M-x sort-fields' except that the text within each line used
     for comparison comes from a fixed range of columns.  See below for
     an explanation.

   For example, if the buffer contains this:

     On systems where clash detection (locking of files being edited) is
     implemented, Emacs also checks the first time you modify a buffer
     whether the file has changed on disk since it was last visited or
     saved.  If it has, you are asked to confirm that you want to change
     the buffer.

then applying `M-x sort-lines' to the entire buffer produces this:

     On systems where clash detection (locking of files being edited) is
     implemented, Emacs also checks the first time you modify a buffer
     saved.  If it has, you are asked to confirm that you want to change
     the buffer.
     whether the file has changed on disk since it was last visited or

where the upper case `O' sorts before all lower case letters.  If you
use `C-u 2 M-x sort-fields' instead, you get this:

     implemented, Emacs also checks the first time you modify a buffer
     saved.  If it has, you are asked to confirm that you want to change
     the buffer.
     On systems where clash detection (locking of files being edited) is
     whether the file has changed on disk since it was last visited or

where the sort keys were `Emacs', `If', `buffer', `systems' and `the'.

   `M-x sort-columns' requires more explanation.  You specify the
columns by putting point at one of the columns and the mark at the other
column.  Because this means you cannot put point or the mark at the
beginning of the first line to sort, this command uses an unusual
definition of `region': all of the line point is in is considered part
of the region, and so is all of the line the mark is in.

   For example, to sort a table by information found in columns 10 to
15, you could put the mark on column 10 in the first line of the table,
and point on column 15 in the last line of the table, and then run
`sort-columns'.  Equivalently, you could run it with the mark on column
15 in the first line and point on column 10 in the last line.

   This can be thought of as sorting the rectangle specified by point
and the mark, except that the text on each line to the left or right of
the rectangle moves along with the text inside the rectangle.  *Note
Rectangles::.

   Many of the sort commands ignore case differences when comparing, if
`sort-fold-case' is non-`nil'.


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