[vtk-developers] vtkTable related problem

[John Biddiscombe]

Jeff

Understood.

I gave up trying to make use of the valid flag and used the empty string 
criterion and what I wanted to do works fine, so it seems I can live 
without the flag for now.

Thanks,

JB
> You are correct, vtkDelimitedTextReader currently creates a set of
> vtkStringArrays as the columns of the table. Once the data is in that
> format (string arrays), everything is valid. Data value validity only
> exists in vtkVariant and vtkVariantArray. We could have decided to
> read data into a collection of vtkVariantArrays instead, and the
> validity information would still be present. The downside of this is
> that vtkVariantArrays are new and generally "unknown" to other filters
> and they tend to not be able to handle them, while vtkStringArrays
> have been around a bit longer and play nicer in the pipeline, e.g. the
> reader is often followed by vtkStringToNumeric (plus there is less
> memory overhead). I could however see the merit in adding an option to
> the reader telling it to create vtkVariantArrays instead of
> vtkStringArrays so this information remains.
>
> Jeff
>
> On Fri, Nov 7, 2008 at 2:44 PM, John Biddiscombe <biddisco at cscs.ch> wrote:
>   
>> I'm guessing Tim or Brian is most likely to know the answer to this...
>>
>> I'm making use of vtkDelimitedTextReader to load a bunch of ascii data into
>> a table.
>> On some occasions, rows of data have fewer/missing entries, so vtkVariant
>> values are generated and inserted into the table during the read process
>> which are 'invalid'. As the data is being read, I can track the valid flag
>> and see that it is preserved as '0'.
>> When I get the output of the filter as a table object and fetch the rows,
>> one by one, I iterate over the values and I find that the values are always
>> valid. even when the rows were half empty in the ascii file. I was hoping to
>> check the 'valid' state so that I could skip certain values and do something
>> special with these rows, but instead, I see a vtkStringArray being created
>> for each column - as I query the row data, the string array returns empty
>> strings with the valid flag set to true for the empty cells.
>>
>> In short, I can test strings to see if they are empty, but I was hoping I
>> could test the valid flag and tell the difference between an empty string
>> and an actually absent value.
>>
>> Can this be done? It seems like the class is protecting itself by replacing
>> invalid data, but at the expense of some potentially useful information
>> specifically
>>   vtkVariantArray *row = table->GetRow(i);
>>   vtkVariant entry = row->GetValue(n);
>> entry.isValid() is always true - even when it didn't exist.
>>
>> Is there another way of getting gthe row/column without the null string
>> creation?
>>
>> thanks
>>
>> JB
>>
>> --
>> John Biddiscombe,                            email:biddisco @ cscs.ch
>> http://www.cscs.ch/
>> CSCS, Swiss National Supercomputing Centre  | Tel:  +41 (91) 610.82.07
>> Via Cantonale, 6928 Manno, Switzerland      | Fax:  +41 (91) 610.82.82
>>
>>
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