On Thu 11-Jan-07 4:21am -0600, Matthew Winn wrote:
> On Wed, 10 Jan 2007 12:19:08 -0600, Bill McCarthy wrote:
>> On Tue 9-Jan-07 4:12pm -0600, Arun Easi wrote:
>>> Lines with same 3rd field are sorted lexicographically.
>>> So, if you have MM/DD/YYYY format, that should be good. If
>>> you have DD/MM/YYYY, it cannot be (Try adding 31/11/1996
>>> and 01/12/1996).
>> Is this documented behavior? It certainly isn't mentioned
>> in the brief docs that come with the GnuWin32 version. Do
>> you have a URL that documents this?
> As far as I can remember sort has always performed that way, using
> the entire line as a "last resort" sort to resolve keys that would
> otherwise sort identically. I have vague memories of seeing this
> documented but I don't know where. I think the idea was that if you
> cared about the order of the lines you'd specify it, and if you didn't
> care then sort was free to use whatever algorithm it chose.
Thanks for sharing that. This time, I googled with "last
resort" included - I found some GnuWin32 documentation.
I went back to the GnuWin32 site and discovered that I may
not have downloaded all the CoreUtils material (I had the
zip file and there is a slightly bigger exe file). I
downloaded and installed. It contains two pdf files I
didn't have before - one with much better documentation for
sort.
There is a very good explanation of the sort:
A pair of lines is compared as follows: sort
compares each pair of fields, in the order specified
on the command line, according to the associated
ordering options, until a difference is found or no
fields are left. If no key fields are specified,
sort uses a default key of the entire line.
Finally, as a last resort when all keys compare
equal, sort compares entire lines as if no ordering
options other than --reverse (-r) were
specified. The --stable (-s) option disables
this last-resort comparison so that lines in which
all fields compare equal are left in their original
relative order. The --unique (-u) option also
disables the last-resort comparison.
It is interesting to note that the penultimate sentence
above appears to imply that the utility uses a stable sort.
A non-stable sort, like quicksort, would not return same key
records in "original relative order" merely because the
last-resort comparison was not performed. Of course, if the
sort switches imply that a last-resort comparison will be
made, quicksort could be used.
--
Best regards,
Bill
