Incorrect values when plotting from file containing time data - gnuplot

Question

I'm trying to generate a graph with gnuplot but it seems that it doesn't show the correct values: Data are:

03/18/2014 15:00:50                32,4
03/18/2014 14:00:48                32,4
03/18/2014 13:00:48               32,42
03/18/2014 12:00:44                32,4
03/18/2014 11:00:42                122,2
03/18/2014 10:00:47                22,4
03/18/2014 09:00:37                53,9
03/18/2014 08:00:35                14,2

The sh is:

#!/usr/bin/gnuplot

set title "Plot x^2"
set terminal png
set output "output.png"

set xlabel "X"
set ylabel "Y"
#set datafile sep ','
set xdata time
set timefmt '%m/%d/%Y %H:%M:%S'
plot 'pepe.csv' using 1:2 with lines

It shows me:

Thanks. I would like that the line have the second value (32,4-32,4-32,42-32,4-28,7-23-6)....The X asys is fine but the second value don't shows the correct values — Luis perez
– Luis perez, Commented Mar 18, 2014 at 15:28
I'm not where those numbers are coming from, is it one column minus the other? Can you edit the question to make it clearer? — Tom Fenech
– Tom Fenech, Commented Mar 18, 2014 at 15:33
I edit the data. The graph is simply a time graph of a tablespace size. Thanks — Luis perez
– Luis perez, Commented Mar 18, 2014 at 15:40
It looks like gnuplot is having trouble parsing both columns of data. Applying the setting set decimalsign ',' may help. — andyras
– andyras, Commented Mar 18, 2014 at 15:45

Tom Fenech · Accepted Answer · 2014-03-18 19:51:29Z

3

@andyras' suggestion of set decimalsign ',' is helpful but if you have a space in the time format then it counts as more than one column. Quoting the documentation:

Each set of non-blank characters in the timedata counts as one column in the using n:n specification. Thus 11:11 25/12/76 21.0 consists of three columns. To avoid confusion, gnuplot requires that you provide a complete using specification if your file contains timedata.

This means that you need to change using 1:2 to using 1:3.

Using your original data, this script works for me:

#!/usr/bin/gnuplot

set title "Plot x^2"
set terminal png
set output "output.png"

set xlabel "X"
set ylabel "Y"
set decimalsign ','
set timefmt '%m/%d/%Y %H:%M:%S'
set xdata time

plot 'decimal.txt' u 1:3 with lines

Output: image showing correct plot

Alternatively, you could use a different data separator in your datafile, such as a , and the time will only count as one column. To do this you add the line set datafile sep ',' to your script.

edit: you might want to also consider using the pngcairo terminal (set term pngcairo), as it looks a lot better:

plot using pngcairo

edited Mar 18, 2014 at 19:51

answered Mar 18, 2014 at 15:58

Tom Fenech

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2 Comments

Christoph Over a year ago

Good guess :) With the pngcairo terminal the graph looks much better i.sstatic.net/XkkPK.png

Tom Fenech Over a year ago

@Christoph I've included your masterpiece

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