Re: multiple plot lines with plot '-'

[<pl...@pi...>]

On 05/19/12 17:37, sfeam (Ethan Merritt) wrote:
> On Saturday, 19 May 2012, pl...@pi... wrote:
>> A test of whether the behaviour is the same would be to use a variable
>> to define the data source:
>>
>> datasrc='file1.dat'
>> plot datasrc, datasrc
>>
>> datasrc='-'
>> plot datasrc, datasrc
>>
>> It would be nice if gnuplot was data source agnostic in that way, but I
>> can see why it was thought to be more useful to treat '-' as a special case.
>
> You should probably add to the mix:
>
>   datasrc="<  date +%N"
>
> All three of these work.  Does that make the program "source agnostic"?

Clearly not , if it does not produce the same result.


> The first will probably produce the same result twice,
> though only if the file contents are unchanged.
> The second may or may not produce the same result twice,
> depending on what is in the input stream.

The second case will 100% _not_ produce the same result , it is plotting 
two different sets of data. Even if the numbers are the same, it is 
plotting different data sets. The behaviour is different.

> The third definitely will not find the same number twice.
>
> It's fair enough to say that the second option, '-',
> doesn't do what you want.

Which is why I was suggesting a new syntax with more compatible 
behaviour. I've now dropped that idea having seen the divergence of 
requirements.

But I don't see the logic for
> calling it a special case.  It's one of several options
> for defining a data source.   Use it only if it is suitable.
>
> Empty quotes '' mean "use the previous data _source_",
> not "use the previous _data_".
>
> Anyhow, I would find it helpful to hear more about the use cases
> where reading data from a separate file is not suitable.
> Is it just a concern that the script and the data will get
> separated?

My initial motivation here was that I have a data file with several 
columns of data. To plot it I need a few lines of gnuplot script to set 
axes labels etc. but it can be done in a couple of lines.

It's too complex to be typed in every time but it is a pain to maintain 
a separate script and data file for such a trivial situation. More than 
one file becomes an 'archive' and requires version matching, etc. A 
single file is much simpler to maintain reliably.

I have gnuplot scripts that run to two pages, there it warrants being a 
file in it's own right, for two lines it's a headache.

The work around you suggested , writing the data out to a second, 
temporary file, would work if we had the  <<EOF perl-like syntax. ( I 
still like that syntax idea. ) But making a file dupe itself seems a bit 
of a  kludge.

Are there technical issues about multiple data files?
> Speed?  Would it solve the problem if you could define a separate
> datablock in the same input file (separate from the 'plot' command
> line)?
>

Yes, maybe defining the data may provide a solution to the case I 
outlined above and may fit in with what Allin is suggesting.

Since the other three input sources produce incompatible results, 
perhaps this one could provide the cached , matrix capabilities that 
Allin was looking for.

Peter.