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Date: Fri, 15 Nov 2013 12:27:12 +0000
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Subject: Re: decimal and builtin _sum function
From: Robert Newson <rnewson@apache.org>
To: "user@couchdb.apache.org" <user@couchdb.apache.org>
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"I store the numbers as strings because I read this the proper way for
decimals."

You'll need a custom library to handle such strings. The article you
read is just pointing out that a string will not be modified or
interpreted in any way, which is the property you seek. But you'll
need a multiprecision library that understands strings of that form to
be able to process them.

B.


On 15 November 2013 12:19, Pedro Narciso Garc=EDa Revington
<p.revington@gmail.com> wrote:
> Yes, I know this is not couchdb stuff. What confused to me was to store
> numbers as  strings.
>
>
> 2013/11/15 Robert Newson <rnewson@apache.org>
>
>> Ah, sure. If you're using floating point to store (or compute on)
>> money values you've committed a sin (I used to work in accounting
>> software, this is the one thing you do not do, besides looking for a
>> job not involving accounting software).
>>
>> We've had a few threads on number handling in the past and it gets
>> complicated. Javascript really only has 64-bit floating point numbers
>> in practice. Our JSON encoder/decoder will retain the precision of
>> your input values but does not guarantee it will preserve the
>> representation.
>>
>> If I were writing accounting software with CouchDB, I would be storing
>> my money values as an object of three strings like
>> {"amount":"200","dp":"2","currency":"USD"}, which represents $2. I
>> would then perform all calculations in custom code, not being prepared
>> to trust the various oddnesses of Javascript.
>>
>> Read https://issues.apache.org/jira/browse/COUCHDB-1410 for more fun.
>>
>> B.
>>
>>
>> On 15 November 2013 11:55, Pedro Narciso Garc=EDa Revington
>> <p.revington@gmail.com> wrote:
>> > Yes, I'm dealing with money but also with micro decrements (cost per
>> > impression on ads).
>> > So my decrements are going to be like 0.000123.
>> > I think what I'm going to do is to sum them before push them into couc=
hdb
>> > so I do not need to deal with decimals.
>> >
>> >
>> >
>> > 2013/11/15 Mike Marino <mmarino@gmail.com>
>> >
>> >> > To answer the original question, _sum can only sum numbers, it does
>> >> > not understand numbers inside strings.
>> >> >
>> >>
>> >> The way I understood the OP's question was that he had correctly,
>> >> following the error message, converted to using numbers instead of
>> >> strings, but then didn't understand the obtained result.
>> >>
>> >>
>> >> >> sidenote: super cool talk by Bartek Szopka about floating point
>> numbers
>> >> in
>> >> >> JavaScript (and other languages) held at JSConf.eu 2013
>> >> >>
>> >> >> https://www.youtube.com/watch?v=3DMqHDDtVYJRI
>> >>
>> >> This is interesting, nice.  I come from a background where numerical
>> >> precision and memory layout is often a concern (e.g. physics
>> >> simulations, hardware readout), but these types of things I think can
>> >> be more easily forgotten when using higher level languages like
>> >> javascript, python, etc.  Imo it's still an essential understanding t=
o
>> >> have.
>> >>
>>