Re: Returning matrices with errors

[Questions r. to t. u. of KeyValue. <key...@li...>]

Hi,

Unfortunately, you can't put a #NULL in just one matrix entry but this
is planned to be possible in the future.

For the time being I suggest the approach given in the code below. In
there, I'm supposing that nRows, nCols are known (size_t's) and your
core library implements a function double calc(i, j) which computes
the (i,j)-th entry of the matrix.

keyvalue::value::Matrix m(nRows, nCols);
for (size_t i = 0; i < nRows; ++i) {
 for (size_t j = 0; j < nCols; ++j) {
   try {
     m(i, j) = calc(i, j);
   }
   catch (...) {
     m(i, j) = something_that_indicates_an_error;
   }
 }
}

For something_that_indicates_an_error I have two suggestions:

1) An obviously invalid value:

For instance, if your matrix is supposed to contain only positive
numbers, then something_that_indicates_an_error could be 0.0,  -1.0,
std::numeric_limits<double>::quiet_NaN() or
std::numeric_limits<double>::infinity().

Unfortunately, for the last two approaches, Excel shows 2.6965E+308
and 1.7977E+308, resp.

2) A string error message:

Recall that keyvalue::value::Matrix entries are of type
keyvalue::value::Variant and, therefore, they can hold the same types
as Variants do. In particular they can be strings. Then, you can set
something_that_indicates_an_error to "" (an empty string) or "Error"
or, "#NULL", if you wish to fake an Excel error.

A remark on the second suggestion. A keyvalue::value::Variant can also
hold a type keyvalue::value::Nothing which indicates no data. My
first idea was letting something_that_indicates_an_error to be this
type but, unfortunately, I just realized that Excel considers it as
0.0. This is not a good thing and I'm going to change this behaviour.

I was wondering to allow keyvalue::value::Variant to hold some type
indicating an error that, latter, Excel would convert to #NULL. I
thought, for instance to allow this type to be keyvalue::RuntimeError.

Any suggestion?

Cheers,
Cassio.

On Wed, Mar 2, 2011 at 9:32 AM, Questions relating to the use of
KeyValue. <key...@li...> wrote:
> Hi,
>
> I have a processor which computes and returns a keyvalue::value::Matrix to
> Excel.
>
> Often, some (but not all) entries of this matrix cannot be computed and my
> core library throws an exception.
>
> In that case the matrix appers in Excel filled with #NULLs.
>
> I would like to catch the exception for any failing entry and resume the
> computations to have the right numbers whenever possible. How can I put a
> #NULL in the failing entries to indicate the failure to the spreadsheet
> user?
>
> Thanks a lot for your help!
>
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