[Qt-interest] Best way to add filter to data

[Konrad Rosenbaum]

On Sunday 27 February 2011, Dan Alcantra wrote:
> I have many table widgets each with their live data feed that adds rows,
> and each with its own schema such as "name, time, value1,value2,..." 
> Under each table I have a text window that I want to allow the user to
> enter simple algebraic expressions to filter out data they do not want. 
> For instance a user might type in "if (name == sensorA)" or something
> like "if (value1< 10 && value2  > 100".
> 
> Rather then create my own interpretor for the algebra I wanted to use Qt
> Script.   I know Qt well enough but how to interface with Qt Script is
> the question.

You need to instantiate a QScriptEngine instance. You either wrap all your 
values as QScriptValues or (easier) you implement a QObject that provides 
them as slots and then add the object with globalObject().setProperty(...).

Then you call one of the evaluation methods to get values.

> Or should I use something else like Perl,

I recommend not to use Perl - it is devilishly hard to integrate. Other 
Languages like Python or Tcl are easier, but each one will need extensive 
integration work.

> or maybe there
> is a C++ library that allows for simple algebra evaluations.  Has anyone
> done something like this ?

I did.

A basic Tcl integration: https://silmor.de/svn/qtkde/qtcl (I never went very 
far with this free (GPL) implementation, but I'm using Tcl in a commercial 
project with great success).

A simple algebraic library: https://silmor.de/svn/elam - it does not have 
advanced scripting capabilities, just evaluating simple expressions and a 
few functions. (It's under LGPL.)

> Any suggestions as to how to start is very much appreciated.




	Konrad
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