gnuplot-info

[Gnuplot-info] Plot command with '-' and '' using same data

[Theo <th...@gm...>]

Hi there,

if I want to include (for some special reason) data into the plotting 
file itself I can use the special filename '-' and write the data in the 
plot file, e.g.:

plot '-' u 0:1 w l lc 1
10
20
30
40
e

If I want to use the data twice and modify it in the second plot I 
thought that I can use the special filename '', which according to the 
manual should "...re-use the previous input file in the same plot command."
The previous input file is '-'. As I understand this data should be re-used.

Factor=1.234
Offset=9.876
plot '-' u 0:1 w l lc 1, '' u 0:($1*Factor+Offset) w l lc 2
10
20
30
40
e

But it doesn't.
I get the message "warning: Skipping data file with no valid points"
Obviously, I have to type in the same data twice:

Factor=1.234
Offset=9.876
plot '-' u 0:1 w l lc 1, '' u 0:($1*Factor+Offset) w l lc 2
10
20
30
40
e
10
20
30
40
e

Why can't I use the same data twice? Can anybody explain?
Is there a way that I have to type in the data only once?

Re: [Gnuplot-info] Plot command with '-' and '' using same data

[Tait <gnu...@t4...>]

The '' syntax re-uses the file name, not the file data. With a normal
file the '' actually re-reads the file again, which is why when gnuplot
goes to re-read from inline you must re-supply the data. To reuse the
file's data, gnuplot would obviously have to cache it, and that is
impractical or impossible for large data sets.

I think I recall some discussion along the lines of implementing a named
data store feature that would explicitly instruct gnuplot to cache a
particular (potentially inline) data set, but I'm not sure whether it
was completed.

To only type in the data once, put it into a regular file with the
appropriate format, and reference it by its file name.

Theo <th...@gm...> said (on 2014/01/22):
> Hi there,
> 
> if I want to include (for some special reason) data into the plotting 
> file itself I can use the special filename '-' and write the data in the 
> plot file...
> 
> Why can't I use the same data twice? Can anybody explain?
> Is there a way that I have to type in the data only once?

Re: [Gnuplot-info] Plot command with '-' and '' using same data

[Theo <th...@gm...>]

Thank you for your explanations.
That's a pity. I didn't want to attach a lot of small separate data 
files to the plotting file. Although it might be possible to somehow 
pack the different smaller datasets in one file but it will not be 
convenient for plotting.

Another approach: Like the variable in gnuplot, can single column data 
be defined in an inline array?
e.g. 'MyValue=3.141' and 'MyArray'=(10,20,30,40,50)
Is this what you meant with "named data store"?


Am 23.01.2014 02:07, schrieb Tait:
> The '' syntax re-uses the file name, not the file data. With a normal
> file the '' actually re-reads the file again, which is why when gnuplot
> goes to re-read from inline you must re-supply the data. To reuse the
> file's data, gnuplot would obviously have to cache it, and that is
> impractical or impossible for large data sets.
>
> I think I recall some discussion along the lines of implementing a named
> data store feature that would explicitly instruct gnuplot to cache a
> particular (potentially inline) data set, but I'm not sure whether it
> was completed.
>
> To only type in the data once, put it into a regular file with the
> appropriate format, and reference it by its file name.
>
> Theo <th...@gm...> said (on 2014/01/22):
>> Hi there,
>>
>> if I want to include (for some special reason) data into the plotting
>> file itself I can use the special filename '-' and write the data in the
>> plot file...
>>
>> Why can't I use the same data twice? Can anybody explain?
>> Is there a way that I have to type in the data only once?
>
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Re: [Gnuplot-info] Plot command with '-' and '' using same data

[Ethan A M. <eam...@gm...>]

On Thursday, 23 January 2014 01:07:39 AM Tait wrote:
> The '' syntax re-uses the file name, not the file data. With a normal
> file the '' actually re-reads the file again, which is why when gnuplot
> goes to re-read from inline you must re-supply the data. To reuse the
> file's data, gnuplot would obviously have to cache it, and that is
> impractical or impossible for large data sets.
> 
> I think I recall some discussion along the lines of implementing a named
> data store feature that would explicitly instruct gnuplot to cache a
> particular (potentially inline) data set, but I'm not sure whether it
> was completed.

Correct.
In 4.7 you can provide named data blocks.

gnuplot> help inline
 There are two mechanisms for embedding data into a stream of gnuplot commands.
 If the special filename '-' appears in a plot command, then the lines
 immediately following the plot command are interpreted as inline data.
 See `special-filenames`.  Data provided in this way can only be used once, by
 the plot command it follows.

 The second mechanism defines a named data block as a here-document.  The named
 data is persistent and may be referred to by more than one plot command.
 Example:
      $Mydata << EOD
      11 22 33 first line of data
      44 55 66 second line of data
      # comments work just as in a data file
      77 88 99
      EOD
      stats $Mydata using 1:3
      plot $Mydata using 1:3 with points, $Mydata using 1:2 with impulses

 Data block names must begin with a $ character, which distinguishes them from
 other types of persistent variables.  The end-of-data delimiter (EOD in the
 example) may be any sequence of alphanumeric characters.

               Ethan


> 
> To only type in the data once, put it into a regular file with the
> appropriate format, and reference it by its file name.
> 
> Theo <th...@gm...> said (on 2014/01/22):
> > Hi there,
> > 
> > if I want to include (for some special reason) data into the plotting 
> > file itself I can use the special filename '-' and write the data in the 
> > plot file...
> > 
> > Why can't I use the same data twice? Can anybody explain?
> > Is there a way that I have to type in the data only once?
> 
> ------------------------------------------------------------------------------
> CenturyLink Cloud: The Leader in Enterprise Cloud Services.
> Learn Why More Businesses Are Choosing CenturyLink Cloud For
> Critical Workloads, Development Environments & Everything In Between.
> Get a Quote or Start a Free Trial Today. 
> http://pubads.g.doubleclick.net/gampad/clk?id=119420431&iu=/4140/ostg.clktrk
> _______________________________________________
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