Re: Re: org-table formulas with missing values

[Rainer M Krug <r.m.krug@gmail.com>]

On Sat, Mar 5, 2011 at 11:55 AM, Thorsten
<gruenderteam.berlin@googlemail.com> wrote:
> Bastien <bzg@altern.org> writes:
>
>> Hi Thorsten,
>>
>> Thorsten <gruenderteam.berlin@googlemail.com> writes:
>>
>>> Ok, trial and error suggests that missing values in numeric columns can
>>> be represented as 0 in formulas, in string columns as "". Is there
>>> something like NaN in calc/org-table?
>>
>> I don't know what is NaN.  Can you give an example of what you're trying
>> to achieve?
>
> NaN stands for NotaNumber and is usually used in statistic programs to
> denote missing numerical values

NaN ia, as you state, NotANumber, but it is NOT a missing value, for
which the abbreviation is NA (Not Vavailable). An example for NaN
would be 1/0 - the value is there, but it is not a number. And,
consequently, NaN and NA can be treated separately. In general, if you
enter values, you use NA, as you usually do not enter values which are
not a number...

> (that deserve special treatment, since
> including them in the calculations as 0 values would not be wise due to
> introduced bias or confusion with true measurements of a value=0).

True.

>
> Fot example:
>
> | day | tel- calls |          change (%) |
> |-----+------------+---------------------|
> |   1 |          7 |                   0 |
> |   2 |          2 |                 -71 |
> |   3 |          3 |                  50 |
> |   4 |            |                   0 |
> |   5 |          2 | round((2/0) 100, 0) |
> |   6 |          0 |                   0 |
> |   7 |          3 | round((3/0) 100, 0) |
>
> #+TBLFM: $3=if(@$-1=0,0,round((((@$-1-@-1$-1) / @-1$-1) * 100),
>  0)::@2$3=@2$2-@2$2
>
>
> Here one measurement (day 4) was missed, one day had 0 tel-calls (day
> 6).
> The change (%) is :
> ((calls day x) - (calls day x-1)) / (calls day x-1) * 100.
>
> The column-formula treats measurment and zero value the same, although
> it would be better to replace the missing value with the average (but
> how to adress it in the formula if not with 0 ?), and it treats the zero
> measurement like a missing value here. Even if there would be no zero
> value here, the missing value would cause a 'divide by zero' error.
>
> I could write 'nan' instead of leaving a blank, and use the string in
> the formula, but this causes errors.
>
> But calc does know the concept of nan: "The variables `inf', `uinf', and
> `nan' stand for infinite or indeterminate values.  It's best not to use
> them as regular variables, since Calc uses special algebraic rules when
> it manipulates them.  Calc displays a warning message if you store a
> value into any of these special variables."
>
> I'm not sure how to use that nan variable in tables and formulas - it
> seems not to be recognized.
>
> Thorsten
>
>
>



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