Re: org-tables with monetary amounts

[Christian Moe <mail@christianmoe.com>]

Hi, Derek,

Very useful, thanks!

Yours,
Christian

Derek Feichtinger writes:

> Hi,
>
> On Mon, Oct 12 2020, Eric S Fraga <e.fraga@ucl.ac.uk> wrote:
>
>> On Monday, 12 Oct 2020 at 10:22, Christian Moe wrote:
>>> I think I was thinking about adding mode flags for unit computations,
>>> like in the imagined example above (`$3=$2+$1;u'), similar to what has
>>> been done for duration computations.
>>
>> This would be very useful, actually.  I use embedded calc all the time
>> with units; being able to use some of the same expressions in a table
>> would be highly welcome.
>
> The functions that one can use in calc formulas can be extended using
> the 'defmath' lisp command. I paste here from my notes (not about
> monetary units, but easily adapted):
>
> +++++++++++++++++++++++++++++++
> Defining a new calc function for unit conversion with defmath
> #+BEGIN_SRC emacs-lisp
> (defmath uconv (expr target-units &optional pure)
>   (math-convert-units expr target-units pure))
> #+END_SRC
>
> #+RESULTS:
> : calcFunc-uconv
>
> | km     | ft           |
> |--------+--------------|
> | 2.5 km | 8202.0997 ft |
> #+TBLFM: $2=uconv($1, ft)
>
> Using the units from the table header (if the 3rd arg is given to
> uconv, the output is stripped of the unit):
>
> |  km |        ft |
> |-----+-----------|
> | 2.5 | 8202.0997 |
> #+TBLFM: $2 = uconv($1 * @<$1, @<$2, t)
>
> The standard calc function usimplify also works for this use
> case:
>
> |  km |        ft |
> |-----+-----------|
> | 2.5 | 8202.0997 |
> #+TBLFM: $2 = usimplify($1 * @<$1 / @<$2)
>
> A lisp equivalent of the above
> #+begin_src elisp
> (calc-eval "usimplify(2.5 km / ft)")
> #+end_src
>
> #+RESULTS:
> : 8202.09973753
>
> Let's define a function that converts to base units
> #+begin_src elisp
>   (defmath ustd (expr) (math-simplify-units (math-to-standard-units expr nil)))
> #+end_src
>
> #+RESULTS:
> : calcFunc-ustd
>
> | distance | time   | speed       | std unit speed   | speed in ft/s    |
> |----------+--------+-------------+------------------+------------------|
> | 3 km     | 2.5 hr | 1.2 km / hr | 0.33333333 m / s | 1.0936133 ft / s |
> #+TBLFM: @2$3=$1/$2::@2$4=ustd($3)::@2$5=uconv($-1, ft/s)
> ++++++++++++++++++++++++++++++++++++