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Re: reliably sort?

• To: mathgroup at smc.vnet.net
• Subject: [mg123656] Re: reliably sort?
• From: Leonid Shifrin <lshifr at gmail.com>
• Date: Thu, 15 Dec 2011 04:51:04 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201112141102.GAA10230@smc.vnet.net>

Union knows nothing about dates. It sorts according to a universal
canonical order, which is
described in the documentation for Sort. You real question then is whether
the Mathematica
canonical order will always coincide with the ordering by date, for your
lists of data. My
first impression is that this is so, but you may want to give it more
thought - there could be
some corner cases. Anyways, my main point is that you can answer this
question unambiguously
by consulting the Sort documentation.

Regards,
Leonid


On Wed, Dec 14, 2011 at 2:02 PM, Michael Stern <nycstern at gmail.com> wrote:

> I have noticed that if combine two lists of date/data objects using
> Union[], the result is sorted by date.
>
> For example
>
> In[]:= mins={{{2001, 1, 31}, 0.993268}, {{2002, 3, 31}, 1.01395},
> {{2003, 6, 30},
>   1.08647}, {{2005, 11, 30}, 1.14752}, {{2006, 9, 30},
>   1.18938}, {{2007, 2, 28}, 1.19658}, {{2008, 1, 31},
>   1.20432}, {{2011, 1, 31}, 1.37501}};
> In[]:= maxs={{{2000, 10, 31}, 1.01816}, {{2001, 12, 31}, 1.02714},
> {{2004, 2, 29},
>    1.12702}, {{2005, 3, 31}, 1.16986}, {{2010, 10, 31}, 1.39026}};
>
> In[]:= Union[maxs, mins]
>
> Out[]= {{{2000, 10, 31}, 1.01816}, {{2001, 1, 31},
>   0.993268}, {{2001, 12, 31}, 1.02714}, {{2002, 3, 31},
>   1.01395}, {{2003, 6, 30}, 1.08647}, {{2004, 2, 29},
>   1.12702}, {{2005, 3, 31}, 1.16986}, {{2005, 11, 30},
>   1.14752}, {{2006, 9, 30}, 1.18938}, {{2007, 2, 28},
>   1.19658}, {{2008, 1, 31}, 1.20432}, {{2010, 10, 31},
>   1.39026}, {{2011, 1, 31}, 1.37501}}
>
> Is this reliable behavior? Is there any case in which Union would /not/
> return results that have been properly sorted by date?
>
> Thank you,
>
> -Michael Stern
>

• References:
  • Does Union[] reliably sort?
    • From: Michael Stern <nycstern@gmail.com>