Re: Sort with -Infinity fails
- To: mathgroup at smc.vnet.net
- Subject: [mg73870] Re: [mg73822] Sort with -Infinity fails
- From: János <janos.lobb at yale.edu>
- Date: Fri, 2 Mar 2007 06:36:20 -0500 (EST)
- References: <200703011117.GAA28248@smc.vnet.net>
On Mar 1, 2007, at 6:17 AM, Tom Aldenberg wrote:
> Dear MathGroup,
>
> Minus Infinity (-Infinity) is smaller than -8, but Sort does not
> sort it as
> expected.
> Is there a Real minus Infinity?
>
>
> In[75]:=
> -Infinity < -8
> Out[75]=
> True
>
> In[76]:=
> Sort[{-Infinity, -8, 5}]
> Out[76]=
> {-8, 5, -=B0}
>
>
> Regards,
>
> Tom Aldenberg
>
> ______________________________________________________________________=
> ______
>
> DISCLAIMER: http://www.rivm.nl/disclaimer.htm
>
Well, being a newbie I looked up sort in the Help. I found that
Sort follows the "canonical Order" - whatever that is. Appendix says:
"Integers, rational and approximate real numbers are ordered by their =
numerical values"
"Symbols are ordered according to their names, and in the event of a
tie, by their contexts"
Lets have the following list:
In[50]:=
lst = {Infinity, -Infinity,
-8, 5}
In[54]:=
Head /@ lst
Out[54]=
{DirectedInfinity,
DirectedInfinity, Integer,
Integer}
So, if you want to have the "normal" result you have to use a
different ordering in Sort to force a numerical value on
DirectedInfinity.
In[53]:=
Sort[lst, Less]
Out[53]=
{-Infinity, -8, 5, Infinity}
J=87nos
========================
"I think I may need a bathroom break? Is this possible?" --G.W.Bush
http://news.bbc.co.uk/2/hi/americas/4249646.stm
- References:
- Sort with -Infinity fails
- From: Tom Aldenberg <Tom.Aldenberg@rivm.nl>
- Sort with -Infinity fails