Thanks again :)
On Wed, Apr 10, 2013 at 1:53 PM, Anthony Scopatz <scop...@gmail.com> wrote:
> On Wed, Apr 10, 2013 at 11:40 AM, Julio Trevisan
> <juliotrevi...@gmail.com>wrote:
>
>> Hi Anthony
>>
>> Thanks again.* *If it is a problem related to floating-point precision,
>> I might use an Int64Col instead, since I don't need the timestamp
>> miliseconds.
>>
>
> Another good plan since integers are exact ;)
>
>
>>
>>
>> Julio
>>
>>
>>
>>
>> On Wed, Apr 10, 2013 at 1:17 PM, Anthony Scopatz <scop...@gmail.com>wrote:
>>
>>> On Wed, Apr 10, 2013 at 7:44 AM, Julio Trevisan <juliotrevi...@gmail.com
>>> > wrote:
>>>
>>>> Hi,
>>>>
>>>> I am using a Time64Col called "timestamp" in a condition, and I noticed
>>>> that the condition does not work (i.e., no rows are selected) if I write
>>>> something as:
>>>>
>>>> for row in node.where("timestamp == %f" % t):
>>>> ...
>>>>
>>>> However, I had this idea of dividing the values by, say 1000, and it
>>>> does work:
>>>>
>>>> for row in node.where("timestamp/1000 == %f" % t/1000):
>>>> ...
>>>>
>>>> However, this doesn't seem to be an elegant solution. Please could
>>>> someone point out a better solution to this?
>>>>
>>>
>>> Hello Julio,
>>>
>>> While this may not be the most elegant solution it is probably one of
>>> the most appropriate. The problem here likely stems from the fact that
>>> floating point numbers (which are how Time64Cols are stored) are not exact
>>> representations of the desired value. For example:
>>>
>>> In [1]: 1.1 + 2.2
>>> Out[1]: 3.3000000000000003
>>>
>>> So when you divide my some constant order of magnitude, you are chopping
>>> off the error associated with floating point precision. You are creating
>>> a bin of this constant's size around the target value that is "close
>>> enough" to count as equivalent. There are other mechanisms for alleviating
>>> this issue: dividing and multiplying back (x/10)*10 == y, right shifting
>>> (platform dependent), taking the difference and have it be less than some
>>> tolerance x - y <= t. You get the idea. You have to mitigate this effect
>>> some how.
>>>
>>> For more information please refer to:
>>> http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
>>>
>>>
>>>> Could this be related to the fact that my column name is "timestamp"? I
>>>> ask this because I use a program called HDFView to brose the HDF5 file.
>>>> This program refuses to show the first column when it is called
>>>> "timestamp", but shows it when it is called "id". I don't know if the facts
>>>> are related or not.
>>>>
>>>
>>> This is probably unrelated.
>>>
>>> Be Well
>>> Anthony
>>>
>>>
>>>>
>>>> I don't know if this is useful information, but the conversion of a
>>>> typical "t" to string gives something like this:
>>>>
>>>> >> print "%f" % t
>>>> 1365597435.000000
>>>>
>>>>
>>>>
>>>>
>>>> ------------------------------------------------------------------------------
>>>> Precog is a next-generation analytics platform capable of advanced
>>>> analytics on semi-structured data. The platform includes APIs for
>>>> building
>>>> apps and a phenomenal toolset for data science. Developers can use
>>>> our toolset for easy data analysis & visualization. Get a free account!
>>>> http://www2.precog.com/precogplatform/slashdotnewsletter
>>>> _______________________________________________
>>>> Pytables-users mailing list
>>>> Pytables-users@lists.sourceforge.net
>>>> https://lists.sourceforge.net/lists/listinfo/pytables-users
>>>>
>>>>
>>>
>>>
>>> ------------------------------------------------------------------------------
>>> Precog is a next-generation analytics platform capable of advanced
>>> analytics on semi-structured data. The platform includes APIs for
>>> building
>>> apps and a phenomenal toolset for data science. Developers can use
>>> our toolset for easy data analysis & visualization. Get a free account!
>>> http://www2.precog.com/precogplatform/slashdotnewsletter
>>> _______________________________________________
>>> Pytables-users mailing list
>>> Pytables-users@lists.sourceforge.net
>>> https://lists.sourceforge.net/lists/listinfo/pytables-users
>>>
>>>
>>
>>
>> ------------------------------------------------------------------------------
>> Precog is a next-generation analytics platform capable of advanced
>> analytics on semi-structured data. The platform includes APIs for building
>> apps and a phenomenal toolset for data science. Developers can use
>> our toolset for easy data analysis & visualization. Get a free account!
>> http://www2.precog.com/precogplatform/slashdotnewsletter
>> _______________________________________________
>> Pytables-users mailing list
>> Pytables-users@lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/pytables-users
>>
>>
>
>
> ------------------------------------------------------------------------------
> Precog is a next-generation analytics platform capable of advanced
> analytics on semi-structured data. The platform includes APIs for building
> apps and a phenomenal toolset for data science. Developers can use
> our toolset for easy data analysis & visualization. Get a free account!
> http://www2.precog.com/precogplatform/slashdotnewsletter
> _______________________________________________
> Pytables-users mailing list
> Pytables-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/pytables-users
>
>
------------------------------------------------------------------------------
Precog is a next-generation analytics platform capable of advanced
analytics on semi-structured data. The platform includes APIs for building
apps and a phenomenal toolset for data science. Developers can use
our toolset for easy data analysis & visualization. Get a free account!
http://www2.precog.com/precogplatform/slashdotnewsletter
_______________________________________________
Pytables-users mailing list
Pytables-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/pytables-users
