gnuplot-info

[Gnuplot-info] Gnuplot is interpolating between missing data

[Dave H. <da...@ho...>]

Gnuplot (on a Mac), 5.4p2

I have some missing data which I indicate with "x" (set datafile missing 
"x"), yet Gnuplot seems to be drawing a straight line between the valid 
data.  Shouldn't it be blank instead?

-- Dave

[Gnuplot-info] Gnuplot is interpolating between missing data

[Dave H. <da...@ho...>]

Anyone?

-- Dave

---------- Forwarded message ----------
Date: Tue, 31 Aug 2021 08:37:08 +1000 (EST)
From: Dave Horsfall <da...@ho...>
To: Gnuplot Mailing List <gnu...@li...>
Subject: Gnuplot is interpolating between missing data

Gnuplot (on a Mac), 5.4p2

I have some missing data which I indicate with "x" (set datafile missing "x"), 
yet Gnuplot seems to be drawing a straight line between the valid data. 
Shouldn't it be blank instead?

-- Dave

Re: [Gnuplot-info] Gnuplot is interpolating between missing data

[Gabriel D. <gab...@gm...>]

Hello,

If you type "help missing" in an interactive gnuplot session, you'll see 
the following:

Gnuplot makes a distinction between missing data and
invalid data (e.g. "NaN", 1/0.).  For example invalid data causes a gap in a
line drawn through sequential data points; missing data does not.

So you should *not* set "x" as the string for missing data. Instead, try 
this:

$DATA << END
1 1
2 2
3 x
4 4
5 5
6 x
7 7
8 8
END

plot $DATA u 1:($2) w linespoints

You'll get a straight line with a two gaps.

I hope this helps.

Gabriel


Le 2021-09-20 à 18 h 45, Dave Horsfall a écrit :
> Anyone?
>
> -- Dave
>
> ---------- Forwarded message ----------
> Date: Tue, 31 Aug 2021 08:37:08 +1000 (EST)
> From: Dave Horsfall <da...@ho...>
> To: Gnuplot Mailing List <gnu...@li...>
> Subject: Gnuplot is interpolating between missing data
>
> Gnuplot (on a Mac), 5.4p2
>
> I have some missing data which I indicate with "x" (set datafile 
> missing "x"), yet Gnuplot seems to be drawing a straight line between 
> the valid data. Shouldn't it be blank instead?
>
> -- Dave
>
>
> _______________________________________________
> gnuplot-info mailing list
> gnu...@li...
> Membership management via: 
> https://lists.sourceforge.net/lists/listinfo/gnuplot-info

Re: [Gnuplot-info] Gnuplot is interpolating between missing data

[Dave H. <da...@ho...>]

On Mon, 20 Sep 2021, Gabriel Dupras wrote:

[...]

> Gnuplot makes a distinction between missing data and invalid data (e.g. 
> "NaN", 1/0.).  For example invalid data causes a gap in a line drawn 
> through sequential data points; missing data does not.

I'd forgotten that; thanks.  On reflection, interpolating missing data is 
indeed the right thing to do (and to think that I gained a Distinction in 
statistics way back in my university days).

> So you should *not* set "x" as the string for missing data. Instead, try 
> this:

[...]

Perfect; that's exactly what I want!  Thanks; I'm not as familiar with 
Gnuplot as I used to be (I really must buy the book).

-- Dave

Re: [Gnuplot-info] Gnuplot is interpolating between missing data

[Kevin O. <rko...@gm...>]

On Mon, Sep 20, 2021 at 3:45 PM Dave Horsfall <da...@ho...> wrote:

> Anyone?
>
> -- Dave
>
> ---------- Forwarded message ----------
> Date: Tue, 31 Aug 2021 08:37:08 +1000 (EST)
> From: Dave Horsfall <da...@ho...>
> To: Gnuplot Mailing List <gnu...@li...>
> Subject: Gnuplot is interpolating between missing data
>
> Gnuplot (on a Mac), 5.4p2
>
> I have some missing data which I indicate with "x" (set datafile missing
> "x"),
> yet Gnuplot seems to be drawing a straight line between the valid data.
> Shouldn't it be blank instead?
>
> -- Dave
>
Not having seen an answer, I'll give it a shot. I believe that this is the
default for gnuplot and that having a missing datapoint entered with a '?'
should do what you want. I've not tried this, but I think that does the
trick.
--
Kevin Oberman, Part time kid herder and retired Network Engineer
E-mail: rko...@gm...
PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683

Re: [Gnuplot-info] Gnuplot is interpolating between missing data

[Norwid B. <nb...@ya...>]

Dave,

based on an entry on stack overflow[1], an input like the following
might fit your needs.  Save it as file ```test.dat```, then run
```gnuplot test.dat``` (in my case, it is gnuplot 5.4.1 which was
good enough, the plot includes the tick for x = 3 but discontinues
the line).

The MWE:
```
set style data lines
set terminal png
set output "see.png"
i=2
plot '-' using (column(i)):xticlabels(1) title columnheader(i)
A B
1 10
2 20
3 ?
4 40
5 50
e
```

credit: [1]
https://stackoverflow.com/questions/22738353/gnuplot-skip-missing-data-points-and-xticlabels 

Norwid