Re: [Gnuplot-py-users] Plotting time formats in gnuplot-py - Question on status

[Michael H. <mh...@al...>]

Thomas Pfaff wrote:

>>Why are you so allergic to temporary files? In most cases they
>>won't be significantly slower, as the bulk of the time is for
>>Python to format the data as ASCII data, which has to be done
>>anyway.
>>
>>Write yourself a little helper function like utils.write_array()
>>but which is smart about date-formatted data. File PlotItems can
>>take arbitrary strings as their "using" argument. What else do you
>>need?
>>
>>    
>>
>Well, basically I didn't like the thought of "having to". In all cases
>regular PlotItems work fine, except for time-data where I would "have
>to" use File PlotItems just because only they would accept the using
>keyword, which seemed to me like some kind of a workaround.
>  
>

What's missing isn't the "using" functionality; it's the ability to 
include date information in data to be sent to gnuplot, and the ability 
to format the date information in a way that gnuplot can read.  
Gnuplot.py uses Numeric arrays to hold the data to be plotted (at least 
when using the Data PlotItem), and I don't know of a good way to store 
date information within a Numeric array.  Therefore the input to Data 
would have to be in a different form to even get started supporting dates.

>Maybe if I understood the concept behind the interaction with gnuplot
>.... If you say that Python has to format the data as ASCII data
>anyway, is it maybe that Python just creates ASCII lines in gnuplot
>format from the data which are then fed to gnuplot via a pipe?
>

That is correct, though depending on your settings the data might be 
transferred inline via the gnuplot command-input pipe, via a named pipe, 
or via a temporary file.

> If I
>can know beforehand how the final line would look like (the data from
>the array marked as x-data would be the first in line, followed by the
>y-data and so on), wouldn't it suffice to have all PlotItems accept
>the 'using' keyword, and then I would just say "using 1:3" if my
>date-strings contained a space?
>  
>

I think the real problem is that dates cannot be expressed as 
space-separated columns of numbers (or can they...?)  Gnuplot.py doesn't 
have a way to output arbitrary strings, at least not via the Data PlotItem.

Let us know what you work out,
Michael