Re: org-tables with monetary amounts

[Christian Moe <mail@christianmoe.com>]

Hi, Daniele,

Good that it's working for you. I'll try to explain the unclear parts.

Daniele Nicolodi writes:

> On 24/09/2020 11:17, Christian Moe wrote:
>
>> Now, with the Calc command to simplify units, you can add dollars to
>> euros and get the result in whichever currency comes first in the
>> algebraic expression
>>
>>   | 3 USD | 4 EUR | 6.58 EUR |
>>   #+tblfm: $3=usimplify($2+$1)
>>
>>   | 3 USD | 4 EUR | 7.6511628 USD |
>>   #+tblfm: $3=usimplify($1+$2)
>
> Having to explicitly use usimplify() is a bit too verbose. It would be
> ideal if this could be somehow be implicit.

Yes, or at least with a less obtrusive syntax, like a mode flag,
something like

  $3=$2+$1;u

(here using "u" for "units" -- unfortunately, capital "U" is already
taken)

>> I don't use this functionality, so I don't have answers to all the
>> questions you'll now have -- including how to get the desired precision
>> without lopping off the currency unit in the last example!
>
> Having the desired fixed precision is quite important for this to be
> useful. In y recent tests I had to drop the units (currencies) to
> achieve this. It would be nice to find a way to avoid it.

[...]

>> Apart from `usimplify', most Calc functions on units appear (?) to be
>> missing corresponding algebraic versions that you can use in Calc
>> expressions in Org tables, which limits the usefulness.

I may be missing something, but it looks like handy Calc commands like
simple unit conversion currently can't be used in an Org spreadsheet,
making Calc units less useful in the spreadsheet. And that this is due
to a lacuna in Calc, not in Org.

When using Calc directly, there are two ways to enter calculations. The
default is reverse Polish notation on the stack (like an old HP
calculator), with various keys bound to all the available commands. The
alternative is algebraic notation.

For example, the command for square root is `calc-sqrt', entered with
the `Q' key. To get the square root of two, you would enter `2 Q' or `2
RET Q'. The corresponding function to use in algebraic notation is
`sqrt'. To use it, you would press apostrophe for algebraic notation,
and enter `sqrt(2) RET'.

But while all Calc commands have keys assigned, it seems not all have
corresponding algebraic notation (?). The Calc manual says that the
command `u s' (`calc-simplify-units') has the algebraic expression
`usimplify'. But it does not list such expressions for other handy Calc
commands, like the `u c' (`calc-convert-units') command, the `u r'
(`calc-remove-units') command or the `u x' (`calc-extract-units')
command.

The Org spreadsheet can also use Lisp formulas, so I've tried to use
calc-simplify-units directly, but this leads to #ERROR.


>> Org tables don't seem to have any specific formula syntax for leveraging
>> Calc unit operations apart from what happens to work out of the
>> box. This might be an area for improvement, though I'm not sure what to
>> ask for.

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. See the manual, 3.5.2 Formula
syntax for Calc. Might be useful, but I'm not sure how to specify a
request.

> I don't understand what you mean in the two paragraphs above. Can you
> please clarify, maybe with examples?

Hope this helps.

Yours,
Christian