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Plot room temperature

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  Plot room temperature Andreas Weller <weller@andreas-weller.de> - 2014-09-24 14:19 +0200
    Re: Plot room temperature Kalin Kozhuharov <me.kalin@gmail.com> - 2014-09-24 07:50 -0700

#2593 — Plot room temperature

Hello.

I'm currently logging my room temperature to a txt file. It is composed
this way:
date in rfc-2822 format + Semicolon separator + Temp.
example lines here:
Wed, 24 Sep 2014 14:08:08 +0200;Temp.: 20.9°C
Wed, 24 Sep 2014 14:10:08 +0200;Temp.: 20.6°C

Now I would like to plot the graph using gnuplot. Please provide me some
help with this - especially the timefmt for rfc-2822...

Thank you!


Regards,
  Andreas Weller

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#2595

Hello Andreas,

On Wednesday, September 24, 2014 9:19:29 PM UTC+9, Andreas Weller wrote:
> I'm currently logging my room temperature to a txt file. It is composed
> this way:
> date in rfc-2822 format + Semicolon separator + Temp.
> example lines here:
> 
> Wed, 24 Sep 2014 14:08:08 +0200;Temp.: 20.9°C
> Wed, 24 Sep 2014 14:10:08 +0200;Temp.: 20.6°C
>
Congratulations on one of the "worst" formats to plot ;-)
Is there any reason why the format is so?
* RFC-2822 is as bad as it can get (search why), use ISO-8601 always
* having a mix of unnamed field (timestamp) and key-value pair (Temp.:20) is a recipe for disaster
* The "°C" might look nice, but it still wreaks havoc in many processing systems (Net used to be ASCII, UTF-8 is far from working everywhere)

> Now I would like to plot the graph using gnuplot. Please provide me some
> help with this - especially the timefmt for rfc-2822...
> 
My approach, if I really had to deal with that, will be to convert it like this:
timestamp,T_C
2014-09-24T14:08:08+0200,20.9
2014-09-24T14:10:08+0200,20.6

then plot it the usual way:
reset;
set datafile separator ",";
set xdata time;
set timefmt x "%Y-%m-%dT%H:%M:%S+0200";
set format x "%Y-%m-%d\n%H:%M:%S";
plot "/tmp/b" u 1:2 w lp

NB: gnuplot doesn't seem to have the notion of timezones... (tried %z before).

Going backwards, you can sidestep some of the timestamp and to plot your original data:
reset;
set datafile separator " ";
set xdata time;
set timefmt x "%d %b %Y %H:%M:%S";
set format x "%Y-%m-%d\n%H:%M:%S";
plot "/tmp/a" u 2:7 w lp

See the weired "u 2:7" ? It is just a hack...

Please consider designing reliable systems; it helps save trees down the road.

Cheers,
Kalin.

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