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Date: Wed, 07 Jan 2009 06:12:01 -0700
From: Eric Blake <ebb9 AT byu DOT net>
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Subject: Re: Inconsistency with sort -n?
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According to Buchbinder, Barry (NIH/NIAID) [E] on 12/31/2008 2:29 PM:

[sorry for my delay in replying]

> `sort -n' and `sort -g' work inconsistently with 0 and -0 if there are le=
ading spaces.  Sometimes -0 is before 0, as I would expect, and sometimes i=
t is afterwards.  Adding `-b' does not seem to help.
>=20
> Is this where I should report it or should I go upstream?

If it were a bug, it would be an upstream issue (I reproduced your test
cases on Linux).  But it is not a bug; sort is behaving as documented.

> $ echo 0 -1 -0 1 | tr ' ' '\n' | sed -e '/^.$/s/^/ /' | sort -n
> -1
>  0
> -0
>  1

sort -n sorts the entire line based on numeric value (0 and -0 have the
same value), then breaks ties based on byte-wise values (' ' comes before
'-').

> $ echo 0 -1 -0 1 | tr ' ' '\n' | sed -e '/^.$/s/^/ /' | sort -g
> -1
>  0
> -0
>  1

sort -g is slower than sort -n, because it converts to floating point; and
although -0.0 and +0.0 are distinct bit patterns, they still sort equal,
so you ware once again back to the fallback of bytewise comparison to
break ties (and ' ' still comes before '-').

Use sort -u to see that 0 and -0 sort numerically equal, and thus why a
fallback sort must be attempted.

$ echo 0 -1 -0 1 | tr ' ' '\n' | sed -e '/^.$/s/^/ /' | sort -nu
-1
 0
 1

Or, go one better - use two sort keys.  Make the primary key sort
numerically, and the second sort key break ties in favor of '-':

$ echo 0 -1 -0 1 | tr ' ' '\n' | sed -e '/^.$/s/^/ /' | sort -k1,1n -k1r
-1
-0
 0
 1

--=20
Don't work too hard, make some time for fun as well!

Eric Blake             ebb9 AT byu DOT net
volunteer cygwin coreutils maintainer


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